If everyone had kids at 18-20, then the grandparents could take care of the grandkids while in their 40s while the parents build their careers from 20-40, then start taking care of the grandkids as the cycle repeats
not really, overall the life expectancy is growing well over 80 years old. unless you live, like, in the woods and feed off berries and hunting or something like that.
and yeah sure there might be somebody that loses their parents at 15, absolutely. i'm sorry for them, but they are not statistically representative in any way.