That exact paragraph is the one I'm complaining about. 31 and 48 are qualified averages (for wealthy landowning males and the same who survived to age 20). "Many lived long past 60" is talking about the outliers of the Templar population. What was the average?
There likely is no average available, as coronors, undertakers, public health departments, and general statistics were poorly kept. So if rigorous comprehensive data are your requirement, you'll likely be disappointed.
What data were available favoured the wearthly, and from them and other, nonstatistical, contemporaneous accounts, it is apparently clear enough to note that the wealthy lived longer lives than the bulk of the population
Many of the poor who died, particularly infants, children, and women, may have left no documentary trace at all.
The average lifespan for a subset of those people who lived to age 20 was 48.
The reason for the distinction is infant mortality and other childhood diseases which lingered much longer than they do today because we now have more treatments.
