boot is right... that was the reason for the low life expectancy...
now a completely different idea:
what if we set a fixed live expectation of 80 years +- 20%? this could introduce methusalem like characters or people dieing at only 60 (without any illness influence that is!)
the only thing we would modify for the different ages would be the risk to die of sicknesses or other typical events.
this risk could also be influenced by living conditions and status (risk when living in city is higher than if living on the land, for nobles the risk is lower than for commons etc.)
this would not include plagues. for a plague it would make no difference if someone is noble or not. therefor plagues will be territorially limited in due to travel restriction until we have aircrafts.
we could define that a plague is triggered in a city if more than 10% of its population get ill
we could also raise the "illness propability" with the age of the character, as old characters are more likely to catch an illness than young ones.
of course specific working conditions (working in a mine for example) could have an influence on the "expected lifespan" of a character.
example:
for a character, his "expected lifespan" was determined to be 70 years upon his birth.
due to him working in a coal mine, the lifespan will be reduced by 20% to 56. this is the MAXIMUM age the character can reach. when coming to that age he dies anyways.
now here is an example for ancient illness propabilities:
age : propability to get ill : propability for death of illness
-10yrs: 10% : 50%
-20yrs: 20% : 60%
-30yrs: 40% : 70%
-40yrs: 60% : 80%
-50yrs: 70% : 90%
-60yrs: 80% : 90%
70yrs+: 90%: 90%
so this chart reflects that in ancient times people got ill more often and the risk to die of this illnes war pretty high.
the chart could look the following way for the modern times:
-10yrs: 10% : 10%
-20yrs: 10% : 10%
-30yrs: 15% : 10%
-40yrs: 20% : 20%
-50yrs: 30% : 30%
-60yrs: 40% : 40%
70yrs+: 60%: 50%
now if our character working in the mine is 40 years old, he would theoretically still have 16 years to live.
but in ancient times he would have a 60% chance of getting ill each TC and a 80% chance of dying of his illness.
in modern times, he would only have a 20% chance to get ill and 20% to die of it.
(the explicit numbers are just an example which must be calculated with some example cases and fine-tuned throughout the game to get the average live expectance we want)
)
and it makes it more real, more characters coming and going. As time and techs come, the life span will increase. 
I have a hard enough time as it is getting everyone to give me stats rather than just saying "so and so had a baby" (with and without the spouse). 
