More likely it was not a problem in getting calories and protein at 20 or 40.
It was probably disease, infection and injury.
Their hygiene was probably horrible. Dysentery was probably rampant.
They drank from water they used for a toilet. They ate raw foods.
They were running from the tiger and fell down the rocks. Broken limbs did not heal.
And that little cut you got yesterday when you were pruning your hedges....that could have killed you.
Life sucked all around back then.
Sure things sucked then - but they’d suck for all ages. What sucked way worse for those at age 30 versus for those for age 20? The differential in suckage would be most great if we’re talking about mano a mano combat.