Well, let's face it - Tony's getting old (just not nearly as old as we are).
With age, connective tissue gradually loses pliability, and articular cartilage shows wear and can more easily be damaged. Anyone of his age playing a contact sport is injury-prone, so the key is to limit contact. The 'Boys have a great OL, and I suspect that protection of the QB is job one.
There's nothing wrong with his throwing anatomy, and that's a big plus. Remember, Peyton had that neck injury with nerve impingement that affecting his right shoulder and arm strength; this is a permanent impairment.
(I hope he wins next week, and can retire on top)
Tony also doesn't have knee, foot, or hip problems, nor does he have an extensive concussion history.
Statistically, his next injury would most likely be a knee. If the OL can protect him, he could last another 2-3 years. If.