How does the depreciating of health with the increase of age account for the average age of peak health? If "Individuals inherit an initial amount of this stock that depreciates with age and can be increased by investment" then that seems to imply that health begins to depreciate as soon as aging begins post birth. But, even without active investment into health as a stock, wouldn't someone in their 20's and 30's be healthier than a baby?
https://www.nber.org/papers/w7078