Tom Brady's decline has begun

Tom Brady doesn't look like the elite quarterback he used to be. Jim Rogash/Getty Images

One of the uncomfortable truths about quarterbacks headed into their late 30s is that the cliff of performance decline can seemingly come out of nowhere in a relatively short amount of time.

Dan Fouts led the league in yards per attempt (YPA) at age 34 then only two years later had the second lowest YPA mark of his career. He called it quits after that season.

Dan Marino led the league in net yards per attempt when he was 35 years old. In each of the next three seasons, he failed to top the 7-yard YPA mark, a statistical feat that happened to him only once prior to 1996.

Fran Tarkenton led the league in touchdown passes and passer rating in 1975 at the age of 35. Two years later, his numbers saw a significant decrease and that drop-off culminated in a 1978 schedule that saw Tarkenton throw 32 interceptions and rank 25th in passer rating on his way to graduating into a broadcasting career.

These are but three of a large number of potential examples that illustrate just how unforgiving Father Time can be at that stage of a quarterback's life.

As painful as it is to say this, after a detailed review of the 2012 New England Patriots season, it looks like Tom Brady, who will turn 36 prior to the 2013 season, will very soon serve as another example of this type of dramatic decline.