[LeBleu]

This is a common misconception caused by quoting mean life expectancy at birth, when the distribution is highly asymmetrical. High infant death rates cause low life expectancy at birth, but the life expectancy if you live to age 5 can be massively longer.

A 5 year old ancient Roman was expected to live to 48. About 35% of the ancient Roman population was over 30 years old. The highest listed age is 76, which is the life expectancy of a 70 year old, an age that about 1 in 50 ancient Romans achieved. http://www.utexas.edu/depts/classics/documents/Life.html

http://en.wikipedia.org/wiki/Life_expectancy#The_Popular_Mis...

[forinti]

Excellent point. But that still doesn't leave many grandmothers around (1 in 3 at best?). And they didn't have many years beyond their reproductive age.

[blahedo]

Um, think about your numbers a bit more. 1 in 3 what? If 1/3 of the population was over 30 and the average lifespan of people living past infancy was 48, there were probably a lot of grandmothers around. Especially if women were having their first children in their late teens, which is just a guess but seems likely.