I've also read it several times before that physicists and scientists tend to achieve their best results by their mid-thirties. But I don't think the characterization necessarily works for physics/math/etc. like it does for baseball and athletics. There's just a major qualitative difference there -- e.g., athletes are forced to retire fairly young, whereas teachers are very rarely forced to retire until they are really nearing the end of their viable lifespan. Although I do agree that in something like physics, there is also a component of "mental athleticism", which just naturally peaks at a medium or youthful age.

Also, for a lot of subjects like physics or math, you probably won't be able to have a decent mastery of your work until around, say, age 25-35. So the simple fact of the matter is that you will always be past your peak for the majority of your practicing career. It's a bit sad, but again, I think it just shows that the concept of "peaking" may not be really as broadly applicable for academic areas.