Large numbers of people living into advanced age is a relatively modern phenomenon. Ten thousand years ago you were likely to die of something like malaria or waterborne illness before reaching your 70s.
For a more recent comparison -- cancer deaths have been on the rise while cardiovascular deaths have been in decline.
The huge jump in average life expectancy has most been the result of babies living to 5 years as apposed to 70 year olds hitting 80. Paradoxically your more likely to see a living great great grandparent 300 years ago than now because people are having children later in life and the increase in 80 year old today has a lot to due with a population boom that happened over that time period.
Not that things are not far better now than at any point in the past, just life expectancy is a poor proxy for ratio of 15 year olds that reach 80. And you have 16 great great grandparent's who all lived to be old enough to have children.
For a more recent comparison -- cancer deaths have been on the rise while cardiovascular deaths have been in decline.