Check out this page I found at beyondveg.com
It goes back much further than the table I referenced in my post on life expectancy in the 1800s. It doesn’t list break down the life expectancy by age, instead listing only the median age for men and women, but it allows for some interesting conclusions when combined with the 1800s data I found previously.
The median life expectancy for men from 1800 to 1920 is listed as 40 years. Remember, median means that half the people lived longer than 40 years, and half died before reaching that point. Based on the breakdown I cited previously, in 1850 over a third of newborns didn’t live to see 10, so it’s clear this is an overall median, including child mortality.
However, median is a funny average. It’s incorrect to assume from the above that primitive man lived into his fifties (assuming he survived his childhood). Again, median simply means that half lived longer, and half died sooner. If the median was 40, it’s possible (although fanciful) to think that a neolithic version of the grim reaper was running around killing everyone who survived to 40 the day after their birthday. It doesn’t seem likely, but it’s possible, and the median wouldn’t be affected. Likewise, everyone who reached 40 (as long as it was exactly half the number of people who were born) could have then lived to Methuselah-like ages, and again the median would still be 40.
That said, it seems reasonable to assume that if the pattern before 40 was similar to that of the 1850s, the pattern after might have as well. If so, it means that people in the 1200s, the 300s, and earlier, if they made it to 20, might have a reasonably expectation of making it to their fifties.
So it’s clear from the numbers that child mortality was a major factor holding down the median lifespan going back hundreds, even thousands of years. Anyone who talks about “average” lifespan without considering child mortality is likely to be dramatically wrong, and anyone who talks about the dramatic dangers of hunting bison/aurochs/mastodons without considering the dramatic dangers of child birth, respiratory infections, and diarrhea is misunderstanding the facts.