Average life span for a Roman in those days was twenty one (21) years of age. I didn’t believe it myself until I looked it up from several different sources.
DariusBane is right. Life span and life expectancy are two different things. Life expectancy is also greatly reduced by infant and childhood mortality.
More info on Roman life expectancy:
https://revealedrome.com/2012/06/ancient-rome-daily-life-women-age/