It's also the optimal age to not have children! You're still figuring out your life, probably no stable partner or job, time to do some stuff you'll regret later, etc.
"Figuring out your life" was not a thing when humans evolved.
> Biological optimal vs societal optimal
to
> Biological optimal vs personal optimal
Put in a catchier way, if nothing is worth dying for, then nothing is worth living for either.
I think you'll find this is a very old viewpoint. As is the smear that we reject any care or duty for society. "This may seem harsh and stubborn and unconciliatory; but it is to treat with the utmost kindness and consideration the only spirit that can appreciate or deserves it."