While browsing the great and wonderful internet, I found the aging curves for testosterone (don’t ask) . It and the hitter’s aging curve are eerily similar to each other.
Testosterone Aging Curve
Hitter Aging Curves (link and link)
I don’t have the knowledge to make too in-depth of conclusions, but some similarities exist. The average peak age and that some players peak later than others are the two likenesses which stick out.