The_Walrus wrote:
For starters, humans don't usually naturally live to "retirement age", so it would be strange for us to have instinctive reactions to that end. We reproduced for a long time when we would basically die as our children left puberty
Um, no. We've been living into our 60s and 70s at least for a very long time, and not just a small minority. Among people who lived to age 20, most would live to 60, with only a minority of people dying in young/middle adulthood. (Higher than today, sure, but still a minority.) You see, mortality by age is not normally distributed, so you can't look at average lifespan numbers and say most people died around that age. For most of human history, two groups had the highest mortality rates - children under 5 and the elderly. In modernized societies, death rates of young children have gotten extremely low, but in societies where 50-75% of newborns don't live to their 5th birthday, they drag down the average quite a bit. (Ancient Rome had an infant mortality rate of about 50%, and that was an improvement on what pre-Roman people had.) For an oversimplified example, imagine if 50% of people died at birth, and the rest lived to age 60. The average life expectancy would be 30 years old, even though none of the population was anywhere close to 30 when they died.
So even in ancient times, most parents lived past their children's twenties, especially since many started families younger. If you have your first child at 15, for example, they'll be 15 when you're thirty, and you'll probably only be halfway through your likely lifespan at that point. Enough time to help raise your grandkids, and maybe even meet your great-grandkids if you're lucky.