Brett Favre had one of his best seasons, statistically speaking, in 2009, throwing a career-low seven interceptions as a starter for the Minnesota Vikings. He was 40.
At 41, Yankees reliever Mariano Rivera is in the midst of his fourth straight season with an earned run average of less than two.
At 37, Bruins goaltender Tim Thomas won the Conn Smythe Trophy as the Stanley Cup playoffs MVP and the Vezina Trophy.
At 38, point guard Jason Kidd -- along with 30-something Dirk Nowitzki -- helped the Dallas Mavericks win the NBA title.
They all were able to compensate for diminishing strength, speed and stamina with consummate skill and experience. The specific athletic demands of each pass, pitch, save and shot -- compressed into a matter of seconds, followed by an adequate period of recovery -- made it possible for them to succeed at the highest levels of their particular craft. They were also blessed with teammates that supported them when they were off their games.
Tennis doesn't work that way.
In this grueling sport where athletes, alone, follow the bouncing ball, 30 is not the new 20. More like 45. The Mayfly, famously, lives for about one day. The shelf life of an elite tennis player, too, is relatively brief. Gravity, inevitably, arrives swiftly.
Bjorn Borg won 11 Grand Slam singles titles, then retired at the age of 25. Legends John McEnroe, Ivan Lendl, Boris Becker and Stefan Edberg all went 0-for-majors in their 30s.
Which brings us to Roger Federer, who turned 30 on Monday.
Federer, through his agent, respectfully declined to be interviewed for this story; great champions, apparently, don't like to discuss the aging process.
Nevertheless, the subject came up in a recent conference call promoting the Olympus U.S. Open Series.
"I'm getting older," Federer I'd rather be 30 than 20, to be honest. To me it's a nice time. In the preparation, nothing changes. Do you listen to your body more? Yes, you do. Are you more wise? Yes, you are. Are you more experienced? Yes. Do you have a thousand matches in your body? Yes, you do.
"You just go with what you have."
In a span of six years, from the age of 22 to 27, Federer played at an astonishing level. He averaged 2.3 major victories per season, equaling Pete Sampras' previous record of 14 in that span alone. The sweet spot was between the ages of 24-27, when Federer won 10 Grand Slam titles, taking three of four in a season on three occasions.
Now the bad news: Federer is 0-for in his last six majors. And, after winning at least one Grand Slam title every year since the age of 21, Federer went 0-for-4 as a 29-year-old.
The numbers, at this stage, are going the wrong way. At this year's Wimbledon, this was excruciatingly evident.
When Federer took the first two sets from Jo-Wilfried Tsonga, his passage into the semifinals seemed guaranteed. After all, Federer's previous record after taking the first two sets was 178-0. But the Frenchman rallied, winning the last three sets by identical 6-4 scores.
"Well," said Federer, "except the score, many, many things went right. I thought I played a good match myself. I'm actually pretty pleased with my performance today."
Indeed, Federer played well, but he had difficulty handling Tsonga's serve and, at times, looked overmatched. It was reminiscent of recent losses in the majors when younger players -- Rafael Nadal, Novak Djokovic, Juan Martin del Potro -- had more game on that given day.
"I think this one for some reason's going to be easier to digest than last year's defeat [to Nadal]," Federer said. "Even though this one was in five sets and I was up two sets to love, I don't really feel like I lost from two sets to love up.
"The game is there," he insisted. "I'm happy. I'm healthy. Even though I took a tough loss today, I don't feel discouraged in any way."
In any way? Coming from anyone else, these would sound like bare rationalizations. Given Federer's record 16 major championships, you probably have to give him a pass here.
"Obviously, his career has been epic from 20 to 30. But he's kept himself in phenomenal health. He hasn't lost a stitch of hair. He plays young."
Some random, 30-centric Federer statistics, courtesy of ESPN.com's research staff:
• In 1999, his first full season, Federer played 30 ATP World Tour matches, going 13-17.
• He lost 30 matches the following year (36-30 overall), his most ever; in four seasons from 2004-07, he lost a total of 24 matches.
• Wimbledon, in 2005, was his 30th career title, and he needed 30 games (16-14) to beat Roddick in five sets in the 2009 All England final.
• His combined year-end rankings, from 2001-10? Yes, 30 -- (13-6-2-1-1-1-1-2-1-2).
If Federer reaches the quarterfinals of this year's U.S. Open, it would be the 30th consecutive appearance in the elite eight of a Grand Slam singles event. The last time he failed to make a major quarterfinal was the 2004 French Open (losing to Gustavo Kuerten in the third round).
Pete Sampras' career offers the best comparison to Fedrerer's because of his major wins and proximity in history. The best Sampras could do in terms of consecutive major quarters was 10, from 1992-94. Ivan Lendl, from 1986-89, put together a run of a dozen. Agassi's best, interestingly, is five. In his last four years, 1978-81, Bjorn Borg reached at least the quarters of all 12 majors in which he appeared (winning seven), but he never played the Australian Open in that time.
Included in that Federer flurry was a streak of 23 consecutive appearances in major semifinals, a ridiculous (and historic) run that was ended by Robin Soderling in last year's French Open quarterfinals.
"The semifinal run to me is the most amazing thing I've ever seen," said Darren Cahill, who coached Agassi and Lleyton Hewitt to the No. 1 ranking. "Records will continue to be broken, but it's hard to believe that one will go. There are two critical elements to this: one, play unbelievable tennis, two, stay healthy. Roger did both."
And, Federer's consistent excellence is still very much in play.
Federer's signature win this season was over Novak Djokovic in the semifinals at Roland Garros. It ended the Serb's celebrated 43-match win streak and brought some fresh currency to Federer's reputation. Afterward, he was asked if it was the best tennis we've seen since he and Rafa tangled in the memorable 2008 Wimbledon final.
"I think I haven't disappeared since, you know," Federer said, sounding a little miffed. "I think I've played some great matches since and I did some sacrifices. I wasn't lying on the beach."
Federer's game, more than anyone playing right now, lends itself to longevity. He is fluid, quiet and efficient. Did we mention that he's played in 47 consecutive Grand Slams?
Nadal, who is five years younger, has already missed Wimbledon (2009) and retired from the quarterfinals of last year's Australian Open with knee issues. He was operating on an injured foot at this year's Wimbledon. The violence in his strokes, the sheer torque he generates, suggests there will be more injuries going forward. Djokovic is the best mover in the game, but his scrambling contortions on the baseline are not conducive to long-term joint health. Del Potro, only 22, won the U.S. Open two years ago, but has already suffered a serious wrist injury.
"Without a doubt," Gilbert said, "this is the greatest top five we've ever had. Man, the guys are all so phenomenal. Rafa has 10 Slams, Djokovic may be having the greatest season we've ever seen. It's not like Fed's not hungry. There is some serious quality there."
Said Cahill, "Everybody's concentrating on Roger. We should be concentrating on the field. Nadal, Djokovic, Murray, Delpo -- those guys are hitting the ball harder and faster than anyone before. And they all move like cats, they fly around the court with great offensive and defensive games.
"That's what Roger is up against."
There is, despite the dire reports, championship life after 30. There are no fewer than 18 30-plus champions on the men's side in the 43 years of the Open era.
The Australians, in particular, found success after professionals were allowed back into the Grand Slams. Rod Laver won all four in 1969 at the age of 30. Ken Rosewall won four majors and reached eight finals -- all after his 33rd birthday.
In more recent years, Andre Agassi's career is worth examining. After wandering into the tennis wilderness for a year or so, he returned with a renewed commitment. Agassi won two majors after his 30th birthday -- the 2001 and 2003 Australian Opens. He also reached two more Grand Slam finals, this time at the U.S. Open in 2002 and 2005.
"I saw it with my own eyes," Cahill said. "If you're looking for a guy to say Roger can't do it, you've got the wrong guy. I mean, look at the history. It is possible."
The guy who beat Agassi in that 2002 U.S. Open final was Pete Sampras, who had just turned 31. Months after that last match, he announced his retirement.
Jimmy Connors had just turned 30 when won the 1982 U.S. Open final over Ivan Lendl. Connors won the Open the following year, too, at the age 31. Arthur Ashe -- five days shy of 32nd birthday -- won the 1975 Wimbledon tournament.
Cahill, who worked briefly with Federer in 2009 before declining a full-time coaching job, believes Federer is not far below his peak in most facets of his game. Has he lost a half step? Cahill says it could be argued -- "slightly," but not significantly.
"Let's just say he's come off his highest level a little bit," Gilbert said. "Maybe he's lost a tiny bit of movement. Maybe a tiny bit less power. It's hard to always be perfect. His level is phenomenal for 30, at No. 3 in the world.
"I won't take away from Djokovic and Nadal. They're five, six years younger. He pushed those guys to another level. Man, the only thing he's guilty of is making the other guys better."
According to Cahill, Federer is an old dog still trying out some new tricks.
The old Federer would come into a match with eight to 10 game plans and go with whatever was working. Now, Cahill said, he needs a very specific plan for the powerful hitters who take the game away from him. With coach Paul Annacone, Federer is trying to be more aggressive, moving forward more frequently when the opportunity presents itself. He is also attempting to be more creative off the backhand side and on the return of serve.
"He used to be happy to get the point started," Cahill said. "Now, he's trying to be more creative, changing position, sometimes running around to the forehand. If you sit around resting on you laurels, you're bound to be disappointed. He's trying some new tactical stuff -- and it's working."
One left in the tank?
If you are an accountant, 30 is early in the curve. Engineers, teachers, lawyers -- they've all got their best years ahead.
Folks around tennis have been calling Federer old for awhile; it began in earnest two years ago in Miami when he cracked his racket during a semifinals loss to Djokovic.
"I told people that we should wait six months after the Australian Open when people thought Rafa and me were done," Federer said after the two met in the French Open final. "It's unfortunate that it goes so quickly at times.
"Now we're back in the finals and now it's different talk again. I don't even go there, because I knew it wasn't the case."
Brad Gilbert isn't buying the Fed-is-done argument; maybe it's because he turns 50 on Tuesday.
"People want to write the obituary," Gilbert said. "I give the guy the next three years, 12 majors in the thick of things. I mean, he's right there. For him, that's what's more frustrating than anything. He isn't some guy who thinks he had a great tournament getting to the quarters -- he wants to win.
"Pete [Sampras] dropped a bit before he won [the 2002 U.S. Open]. I don't think Fed's done."
Gilbert, who loves to tinker with numbers and the laws of probability, thinks the over/under for Federer's future Grand Slam singles titles is 1.5.
Cahill, too, is thinking that way.
"You obviously won't see the domination of years ago," Cahill said. "I thought the French Open was his least chance to win a major. After seeing , you have to believe he can still win any of them."
Federer, too, agrees.
"It's nice to talk about something more positive, [rather] than saying after a certain time or when you have kids you can't win anymore like many people tend to say or talk," Federer said. "But I think I don't want to say I'm a special case, but I've won so much you feel like if you put yourself in the right position, you do all the right things, you'll definitely get a shot again of winning any big tournaments, or any tournament really for that matter.
"I always said, inspiration for guys that play for a very long time, like Andre Agassi, Jimmy Connors, Ken Rosewall, Rod Laver, it's very inspiring to see what they've been able to do for a
very long time. I'm looking forward to see how much I can achieve from this point forward, for sure."
Federer was almost upbeat after losing to Nadal in this year's French Open final. It's almost as if he surprised himself.
"I'm feeling better physically than I have in a long time, so it's been very positive," Federer said. "Overall, obviously, I'm very happy with the tournament.
Added Cahill, "A guy that plays like Roger does is capable of stepping into the big occasion. It's not the same [level] day in and day out as it used to be. It just has to happen a few times at a Slam and he's got another title.
"If I have three windows -- one, two, three -- I'll take window No. 1. I really believe he'll get one more."
Greg Garber is a senior writer for ESPN.com.