For the the recent The Hardball Times Annual, Brian Cartwright and I wrote a piece on Tommy John surgery. An aging curve on was cut from the article. I feel it provides significant insight so I will provide it now.
Pitchers generally get worse as they age with the one exception being that pitchers see an improvement in their walk rate until age 29. TJS pitchers show more year-to-year volatility, but over the long run the values stay the same, unlike the general pitcher population, which sees its values degrade. It is almost like the pitchers are getting a new throwing arm or at least a new ligament in the arm. Some survivor bias is present, as only pitchers that were able to return to pitch at a competitive level are shown. The bias exists with the overall aging curves, but not as much as those that have had Tommy John surgery.