“What was the average life span back then?”
Basically 60+, but only if you made it to age 20, which was less than half of the people born, but then the birthrate was far higher than today’s birthrate.
The main reason for not people not getting dementia was that no one took statins, and thus their brains received the high levels of cholesterol needed to operate properly.
Good to know because my level of cholesterol would make me a Mensa candidate.