"Lifespans were short, so there were basically no old people."
I don't have a citation for this, but I've heard that the reason that the average lifespan in ancient times was so short was mostly due to the high rate of infant mortality.
Those people who did manage to survive infancy actually lived much longer than you'd expect. And the maximum human lifetime back then was not much different than the maximum human lifetime today.
I don't think KK is talking about averages that have been brought down by infant mortality. He's saying explicitly that among hunter-gatherers, lifespans were short. Which I believe from what I've read about them.
It's also false that people who made it to maturity in preindustrial times lived as long as people do today. It was unusual to see 70.
I don't have a citation for this, but I've heard that the reason that the average lifespan in ancient times was so short was mostly due to the high rate of infant mortality.
Those people who did manage to survive infancy actually lived much longer than you'd expect. And the maximum human lifetime back then was not much different than the maximum human lifetime today.