Tomorrow is coming more quickly than the Colts and their fans like to admit. In that tomorrow, there is someone under center who does not wear No. 18. The team acknowledged as much last winter and spring as they went through the pre-draft process with a careful eye on quarterbacks, and identified two or three they had serious interest in, but did not end up taking one. Peyton Manning is 35-years old, but the hope is that he can play at a high level for at least another four years. “I don’t think he is on a short time frame in terms of quality play,†Colts president Bill Polian told Dan Pompei of the National Football Post. “I think four years is an absolute certainty barring injury. It could go beyond that. He believes he can go beyond that. I wouldn’t argue with him. I believe everything he says. This is not something that has to be imminent.†This offseason, Manning did undergo a second neck surgery in as many years, but the Colts are not concerned about his disc issues. “All I can tell you is I can only go by what our doctors tell us,†Polian said. “They said were he not a football player, they would have simply treated him with traction. The fact that they performed a procedure was almost a fail-safe type thing. They don’t consider it career threatening or debilitating.†Source: National Football Post
I think Manning is one of those guys who, with his knowledge, could play a role in the league well into his forties. However, having watched his arm regress the last two seasons (Go ahead and flame me, but he's lost a bit of zip on his passes and accuracy hasn't been too hot either), I think Manning's time as an elite QB is coming close to the end.
He can play for four more years, but he will be playing as an average starting QB in 2 or 3. He's losing his touch.
What he lacks in arm strength, he'll be able to make up with his mental game and extend his career further than the normal QB would.
Honestly, I think that 2010 was the beginning of the end for Peyton Manning. I read an interesting study somewhere a couple of years ago that detailed the arc of performance by the league's top QBs during the Live Ball Era (1978-present), and most QBs' performances began to drop markedly starting at age 34. Manning turned 34 last year. I give him four more years in the NFL, but it'll be clear by the end of 2012 that other QBs have passed him by. By the way, Tom Brady turns 34 this year, so New England's window for a championship is smaller than people realize now.