> All we have from those times are a few bone samples and a few anecdotes preserved in fragments. This is the bit that you're missing: antiquity is generally c

> All we have from those times are a few bone samples and a few anecdotes preserved in fragments. This is the bit that you're missing: antiquity is generally considered to extend all the way into the 500-600s AD, with the Roman empire dominating its center and 'late antiquity' covering the whole early period of the Byzantine empire. This means that even just in Europe we have extensive documents (e.g. in the Christian era, baptism and burial records), as well as a wealth of burial evidence from which to extrapolate lifespans. If you look into the sources for Rome you'll find Egypt in particular come up a lot, which isn't an accident: the dry climate and extensive use of papyrus means that the region preserved far more records (and bodies) than any other part of the empire.