Today I learned

It is true that mean life expectancy in the Middle Ages and earlier was low; however, many take this to mean that people usually died around the age of 30.

In fact, the low life expectancy is an average very strongly influenced by high infant mortality, and the life expectancy of people who lived to adulthood was much higher. A 21-year-old man in medieval England, for example, could by one estimate expect to live to the age of 64.

From: List of common misconceptions (Wiki).