Yes, the average human lifespan has been increasing for the last bunch of years, basically due to the increase of better health care. However, even in roman times, there were a number of individuals from the high classes of soceity that had the better environment to live, and therefore lived into their 80's and 90's.. so the potential has not increased.
Ramoss, I think then as now the primary improvement pushing longer life spans was simply a matter of sanitation and clean water supply. Some very basic principles of human waste disposal and safe water distribution allow the opportunity to reach a genetically-limited age--even today millions die from the diseases that are rampant without rational sanitation practices. Dysentery ravages infants and children in the less developed world.
Invictus, while there have always been some children born to older parents, the percentage is small. Selection doesn't get much opportunity to operate on genes for longevity because prime reproductive years are youthful years. Also, the probability of defective genes increases in aging germ cell lines, e.g., Downs' syndrome among the infants of older mothers, and, recently, a correlation established between having an older father and being at risk for schizophrenia.
The diseases of advancing age--atherosclerosis, cancer, dementia, etc.--have not been strongly selected against because they have little or no impact on reproductive fitness.
Some theorists have argued that elders who survive longer provide an advantaqe to their group via culture/memes to explain why we live past our prime reproductive years. The onset of menopause rather than child-bearing unto death is sometimes cited as an example.
It occurs to me that the near universal tendency for old dominant males to obtain young mates might play some part in conserving longer life spans, but I think I'll say no more about that.
Edited by Omnivorous, : Typo. I'm old, I can't help it.