First, the age of the Roman republic was a long way from the stone age. Second, by then grain was a HUGE part of the diet, so drawing conclusions about life expectancy from Roman traditions is probably not a great example. Third, Romans didn't live that long - here are a list of emperors I could find who died of natural causes...
Augustus - 75
Tiberius - 77
Vespasian - 69
Titus - 41
Nerva - 67
Trajan - 63
Hadrian - 62
Antoninus - 74
Marcus Aurelius - 58
I'll stop there - the next century is a drag.