Not sure how to get to that link, but from what I have seen in my many years of watching and reading about the game, throughout major league history a very low percentage of pitchers have even been still pitching at Mussina's age, and even fewer have actually shown a vast improvement as they are closing in on 40. (Clemens is one who did, but his records are highly suspect, considering the evidence that he juiced. The pre steroid era was different).
Kudos for calling Mussina's resurgance in March, I could have sworn he was finished. (And I wish he were, I have not forgotten how he left the O's to go to the Yankees of all teams)