That opinion came to light when some of the Patriots quarterback's personal correspondence was made public this week as part of the Deflategate lawsuit.
"I've got another 7 or 8 years. He has 2," Brady wrote last November in an email to a childhood friend. "That's the final chapter. Game on."
While that note pours another can of gasoline on the Brady-Manning rivalry, it also speaks to Brady's supreme confidence in himself. Brady turned 38 earlier this week, so he's predicting he will play until age 45 or 46.
While Brady waits for his federal case over his Deflategate suspension to be adjudicated, let's look to the history books to rate his chances of career longevity.
There are 18 quarterbacks in NFL history who have thrown a pass in a game at age 40 or older, according to the Pro Football Hall of Fame -- and zero have started a game at age 45 or older.
Here's how those 18 QBs fared in their 40s, grouped by their age in their final NFL season:
George Blanda, Oakland Raiders: Blanda is a Hall of Famer and the oldest player in NFL history, but he was primarily a kicker for the last decade of his career. Blanda didn't start a game at QB after age 41.
Warren Moon, Kansas City Chiefs: Moon is a Hall of Famer who played effectively until age 42. He made the Pro Bowl with the Seattle Seahawks at age 41 in 1997 after leading the league in passing yards per game. His last start came at 44, when the Chiefs handed the 2000 San Diego Chargers their only win of the season.
Vinny Testaverde, Carolina Panthers: The former No. 1 overall draft pick enjoyed a productive 21-year NFL career and was named to the Pro Bowl at ages 33 and 35, with the Baltimore Ravens and New York Jets, respectively. He started six games for the Panthers at 44 in 2007, producing a 65.8 passer rating.
Steve DeBerg, Atlanta Falcons: DeBerg was a dependable, if unspectacular, player from 1979 to 1993. After retiring at age 39 and sitting out four seasons, he joined the Super Bowl-bound Atlanta Falcons in 1998. He started one game that season, going 9-for-20 with an interception as Atlanta lost 28-3 to the Jets.
Doug Flutie, New England Patriots: The 5-foot-10 Flutie defied doubters to enjoy a two-decade career in the USFL, NFL and CFL. Flutie threw for 985 yards with nine touchdowns and four interceptions at age 41 while replacing the ineffective Drew Brees in five starts for the 2003 San Diego Chargers. His final career start came the following year with San Diego. He finished his career as Brady's backup with the 2005 Pats, going 5-for-10 in spot duty and scoring an extra point on the NFL's first successful dropkick in 55 years.
Earl Morrall, Miami Dolphins: Morrall started nine games for the undefeated 1972 Dolphins at age 38. He started one game in each of the next three seasons in place of Bob Griese and last played in 1976.
Brett Favre, Minnesota Vikings: The three-time MVP produced arguably his best statistical season -- with a passer rating of 107.2 -- in leading the 2009 Vikings to the brink of a Super Bowl appearance at age 40. He regressed considerably in his final pro season, posting a 69.9 passer rating with 19 interceptions in 13 starts the following year.
Mark Brunell, New York Jets: Brunell stayed in the league as a backup until the 2011 season, but his last year as a starter was with Washington in 2006 at age 36. Brunell's best seasons came with the Jacksonville Jaguars, where was named to three Pro Bowls and led the team to two AFC Championship Games. Brunell, now an ESPN analyst, criticized Brady in the wake of Deflategate accusations. In another email made public this week, Brady wrote, "He's a patriot hater. They all are!!!" about Brunell to a friend.
Charlie Conerly, Len Dawson, Vince Evans, Joe Ferguson, Jim Hart, Brad Johnson, Sonny Jurgensen, Dave Krieg, Johnny Unitas and Wade Wilson: The most successful age-40 season of this group was from Jurgensen, a Hall of Famer who went 3-1 in four starts for Washington in 1974. Unitas, also a Hall of Famer, ended his career ignominiously by going 1-3 in four starts with the Chargers.
It's important to note that QBs are now protected more than ever by rules changes -- a 2009 stipulation to protect passers' knees is widely known as the "Brady Rule," because it followed his ACL injury at the hands of Bernard Pollard. So Brady clearly has a better opportunity to remain healthy deeper into his 40s than players of yesteryear. He simply won't face the same level of physical pounding as his predecessors.