How much longer will Brady be elite?

On Tom Brady's 35th birthday, it seems appropriate to reflect on how many seasons Patriots fans can expect the quarterback to keep performing at an elite level.

Over the last five seasons (not counting 2008, which he missed with a knee injury), Brady has averaged about 4,584 yards and 38 touchdown passes per season, including a career-high 5,235 yards passing last season, which would have been an NFL record if not for Drew Brees' 5,476.

If Brady plays to those averages this season, he’ll either set or approach NFL records for touchdown passes (Randall Cunningham, 35 TD tosses in 1998) and passing yards (Warren Moon, 4,690 in 1991) in a single season for a player age 35 or older.

Considering his current good health and the Patriots’ talent at the receiver and tight end positions, there’s no reason to believe those numbers will dip this season. But Father Time will eventually catch up with Brady, that much is inevitable.

So when should we expect a dropoff?

For that answer, we looked at how some comparable modern-era quarterbacks fared at age 35 and beyond. Specifically, we examined the late-career performances of Brett Favre, Joe Montana, Dan Marino and John Elway.

There aren’t many definitive conclusions you can draw from the numbers, aside from the fact that their touchdown numbers dipped slightly (save for Elway), though their passing yardage totals actually increased on average.

The fact remains, however, that one of these years, Brady’s performance is going to start to dip. After all, only four quarterbacks have won Super Bowls after age 35 (Elway the latest; he did it twice).

Brady is under contract for the next three seasons, leaving him a 38-year-old free agent before the 2015 season (unless, of course, the Pats re-sign him before then). Will he still be calling signals in New England at that point?

Montana and Jim Kelly retired when they were 36. Marino, Elway and Steve Young were each 38 when they decided it was time to quit. Favre played until he was 41. Moon outlasted everyone, finally retiring at age 44.

Brady’s shelf life is a topic that is only going to become a bigger issue as the years go on. So on today, his 35th birthday, we ask you: How many more seasons do you think Brady has left? How many more seasons will be able to perform at an elite level? Vote in the poll above and share your thoughts in the comments section.

ESPN Stats & Information contributed to this report.