If you take a look at the most reliable source of information in all of the green planet, ie.. wikipedia, http://en.wikipedia.org/wiki/Life_expectancy quotes some interesting figures for how life expectancy has improved in the past many many years. Here's an excerpt for your convenience:
Neolithic 20
Bronze Age 18
Classical Greece 25-45
Classical Rome 25-45
Medieval Britain 20-30
Early 20th Century 50
Current world average 67
Now this chart really astounded me. The immediate inference ofcourse is that we have done the following to varying degrees:
1) Increased our natural immunity (exercise, eat and drink healthy)
2) Improved our surroundings to suit our bodies
3) Improved artifical immunity and recovery (medicine)
4) Increased infantile rate of survival (again medicine)
5) Reduced death due to war (not sure if this makes a big diff.)
But the more interesting thought that occurred to me was on wisdom. We always attribute a lot to the wisdom of our forefathers. If the average population lived much lesser years than us, does this stand to reason that the age at which folks started to be called experienced and wise and started doling out advice was lesser? Imagine the bronze age, a 12 year old would have had the worldly wisdom of a 50 year old in out time. Remember that although we are more advanced now, the amount of discoveries and inventions in their time would have been just significant to them as those we have made recently. So "worldly wisdom" wise, I see no problem in making that connection. Also, during the Greek and Roman times, if the life expectancy was 25-45, it stands to reason that 15 year olds were probably fighting in wars. Finally, anyone older than this margin, woudl automatically be an elder meaning Britain probably had 32 year old elders. When I hear the word elder I imagine a person with long white beard, wrinkles in his face and struggling to walk.