More injuries at 30 than at 20. And the ability of the body to heal is better at 20 than at 30.
Think we are saying the same thing.
It also probably depends on a social structure. Elder males may have been respected for their knowledge and life experience and had to compete less with the younger males.
If the cut off age were 40 or 50 I could buy the infection, or healing theories. Given that the cut off is 30 my argument is that what really drops off fast between 20 and 30 is athletic supremacy as we see in today’s such biologic experiments. That is where you see a steep drop off starting to happen around age 30.