Original sentence: The "bottom line" is that there is no reason to believe that there couldn't have been a few men/women in a population of 2,500 years ago who were centenarians, even if they weren't commonplace.While ancient demographics are biased in favor of wealthy or powerful individuals rather than the ordinary person, it is unscientific to suggest that "ordinary persons" lived longer.While the  density of centenarians per capita was much less in(civilized) ancient times than today, the data suggest that age 100 was not impossible then
Edited sentence: It's just that there has never been any good documentation for ordinary people who were not already famous for some reason or another, so all the demographics are biased in favor of wealthy or powerful individuals rather than the ordinary person.The "bottom line" is that there is no reason to believe that there couldn't have been a lot of men/women in a population of 2,500 years ago who were Centenarians, even if they weren't commonplace.Therefore, I would speculate that the density of Centenarians per capita may well have been the same in (civilized) ancient times as it is today