“...when people that were 40 were at death’s door from old age”
That’s a common misconception. A 40-year old in 1790 wasn’t considered “at death’s door” anymore than now. He wouldn’t have grey hair or stiff joints. Today many more people make it to their 70s than back then but that’s largely due to the very high death rate of the very young. Old age then was pretty much what old age is now—it’s just that lots more people today get to enjoy it.