>>6
Life expectancy estimates actually say little about how long people in a given era lived, unless one looks at them in detail. Why? Because average life expectancy for a society is life expectancy at birth. In a society with fairly high infant and child mortality rates (most pre-modern societies, most less developed modern societies), life expectancy at birth is low, but once one has survived into adulthood, one's chances of living to a decent age are pretty good, and the longer one lives, the higher is one's life expectancy (because one has outlived the cohorts that drag the figure downward and is now among the cohorts that raise it).
The Juliet issue is a different one: in many pre-modern societies, age of first marriage was low, especially for girls (Catholic Canon Law, which influenced marriage law of much of Europe and elsewhere into the modern period, based its minimum age of marriage on Roman law, which itself seems to have been based on general ideas about puberty, and so set it at 12 for girls), and age differences between spouses were often large.