Counter example https://en.wikipedia.org/wiki/Demography_of_the_Roman_Empire https://en.wikipedia.org/wiki/Demography_of_the_Roman_Empire What's important is t

Counter example https://en.wikipedia.org/wiki/Demography_of_the_Roman_Empire https://en.wikipedia.org/wiki/Demography_of_the_Roman_Empire What's important is the life expectancy at a given age. There used to be a huge infant mortality but the half of newborn that made it to 10 would live on average 50 years. That means that some of them would live 70 or more. There is a table with life expectancy given the age. At 70 was 6.5 more years. That is from a mix of the sparse available data and models.