I don't have my Historical Baseball Abstract handy, but I know Bill James' research in that book supports the 26-27 peak. The Baseball Prospectus crew is also on board that age range. In fact, that age range seems widely accepted to me in baseball research circles at the moment and not the hotly debated topic you suggest it is. I do agree that there are outliers -- both late and early bloomers. And it's possible that Lee is one of the former. I also think it's reasonable to expect Lee's numbers to drop next season based on his age and career numbers to date. LOL, ok as I eat crow here I hope I don't choke... I realized what I wrote while having lunch. Bill James does not support 28-32 as prime in fact, he was a driving influence of Beane, the A's, Alderson, et al, in crafting rosters of so called peak performers. However, prior to James' Abstract in 1982 it was widely accepted that the prime age of baseball players was 28-32. He along with Money Ball helped to change that idea. James wrote the following: In all fairness, there are writers and executives alike that believe the peak extends into the 30's and as such it is hotly contested. Furthermore, there are many Baseball people who publically and not so publically denounce the ideas behind Money Ball. Afterall, the backbone of the "diminished returns" theory is more economically based than purely based on athleticism and ability.