From my genealogy research, people lived very long if they managed to get past childhood deaths. I have lots of 16th century ancestors in their late 70s and 80s.
That is what I have read as well, from documents in the Middle Ages in England, I read in a book a few years ago. Once a person made it through childhood, and if a woman, through the child bearing years, 70s and 80s were not uncommon at all.
Your correct, my genealogy research shows many ancestors who lived into their 80s and 90s.
Our founding fathers didn’t worry about age limits; they believed that the voters would elect honorable, capable, and patriotic men and that those elected would appoint the same.
That is one concept that did not last very long.
Yes, from my own reading it appears that the reasons for the markedly shorter average lifespan back then are more related to infant/childhood mortality and accidental death than shorter lives.