Is Federer approaching the end?

They say age is just a number, and sometimes it's not even that.

It was Boris Becker who famously said players' careers could be measured in "dog years," but the calculations differ depending on the player. Someone such as Tommy Haas, who missed significant playing time with injuries and surgeries, is perceived as a "young" 35. It was the same with Andre Agassi, whose up-and-down, on-and-off career seemed to help him remain at the top until he was 33.

Conversely, precocious pros or intense workers such as Michael Chang or Jim Courier are often seen as further along in their careers than their actual ages might suggest. So, as the sport becomes increasingly preoccupied by what 32-year-old Roger Federer's prospects are going forward, it's a good time to ask: How old is Federer, really?

One way to calculate that is by the number of matches a player has logged in his career. Like mileage on a car, it's a rough indicator of wear and tear. As with mileage, it doesn't show everything -- the length and competitiveness of the matches, the training done for them, how they were scheduled, and the level of pressure are also involved. But it might be a more telling measure than simply counting birthdays.

So what does Federer's odometer show? A lot of miles.

Although Federer came into the US Open as one of 11 men in the draw aged 32 or older, he was by far the oldest in terms of matches at the pro level. The 17-time Grand Slam champ had played 1,119 ATP matches in his career coming into the tournament (winning 910), and a total of 1,177 on the tour and minor leagues.

Meanwhile, Haas -- the oldest player in the draw and about 3 years and 4 months older than Federer -- stood at 883 matches, or about three-quarters of Federer's total. Michael Russell, also 35, came in at 802 matches, most of those at the minor league level.

Lleyton Hewitt is another 32-year-old former No. 1 still playing on tour, but Hewitt peaked and declined much earlier in his career, and has also had much more injury trouble than Federer. He has played 862 matches.

Federer, of course, has played more because he has won more. His legendary consistency -- 10 straight years in the top four in the rankings-- means he has racked up not just large numbers of titles and records but of matches, as well. (Rafael Nadal, five years younger, is roughly on the same track with 866 matches.)

It also means that many of those matches have come in bunches, on back-to-back days or a day apart at the same tournament, requiring more stamina than playing a round or two each week. A disproportionately high number have also been five-set matches.

Federer just played a record-tying 56th consecutive Grand Slam tournament; holds the record with 10 straight finals, 23 straight semifinals and 35 straight quarterfinals at majors; and was playing back when a few Masters tournaments also had best-of-five finals.

Moreover, those kinds of big matches come with extra pressure and tough opponents. A regular match is no walk in the park, but playing the likes of Nadal, Marat Safin, Novak Djokovic and Andy Murray over five sets is a different animal altogether. Competing at the top takes its own toll.

Even compared with other greats, Federer's match count is high. It's quite a bit more than the 984 matches Pete Sampras played in his career before his last match at 31, and even more than the 1,154 Agassi had when he retired at 36. But it's still well back of Jimmy Connors' official mark of 1,426 matches when he retired at 40, or Ivan Lendl's 1,310 when he stopped at 34, showing that more remains possible.

Although determining match records is more difficult for players further back, others who have set benchmarks for longevity include Ken Rosewall, who won his last Grand Slam at age 37 in 1972, and Pancho Gonzales, who played a classic five-setter at Wimbledon when he was 41.

But the physical demands of the game have increased greatly in recent years, and even though players seem to be playing longer than a generation ago, competing on tour requires more training and fitness work than ever. That also means extra impact on the body.

Although most of this suggests that Federer might be even "older" than his relatively advanced tennis age of 32, there are also considerations that help keep him "younger." His fluid, seemingly effortless game has helped keep him remarkably injury-free over the years, and he has planned his playing schedules carefully and been meticulous about preparing properly with the services of a physiotherapist and a fitness trainer.

His enthusiasm for playing, practicing and traveling is not to be discounted, either.

Paul Annacone, who has coached Federer and Sampras, compared them last year, saying, "Roger is much more in the middle of his career at 31 than Pete was at 31. Roger, with all due respect to the smaller tournaments, wins a small tournament and is emotional and loves it, where Pete -- I don't want to put words in his mouth, but Pete would be, 'Why are you even playing that tournament?'"

Federer is aware of the extent to which players have been able to push time limits on their careers.

"[I]t's definitely an inspiration seeing guys being around for a long time like Ken Rosewall, Jimmy Connors, Andre Agassi, and then there are tons of other players who were there for a long time," he said at the US Open a couple of years ago. "I feel my game allows me to, you know, still play for many more years because I have a relaxing playing style. I have almost played a thousand matches on tour [at that time] and that leaves its toll, but I'm very professional when it comes to massages, stretching, diet, sleep, all of that stuff. So I have always looked in the long term as well for a long time.

"That's why I'm confident I can still play for many more years to come at the highest of levels."

But his poor performances this season have created doubts, at least among others. Back problems and fatigue-related off days have become more frequent, and experiments with a larger racket frame suggest Federer himself feels things are no longer quite the same.

Part of the problem has been the disruptive effects of injury, but it remains to be seen whether the situation is temporary or a regular part of the picture from here on. Yet there have also been signs, when everything is right, that he can still hit the high notes.

Whatever happens, the match records reveal that Federer is now at a stage where very few players have been before -- trying to remain competitive at the top past the 1,000 matches mark. A career that has reached the greatest heights is now trying for great length, as well.