This is true, but not in the way that you think... WE ARE NOT LIVING ANY LONGER THAN WE DID IN 1900!! Look at the data; the average life expectancy has increased from around fifty to around seventy-six, for a new born. For someone who is sixty, the average life expectancy is about the same. This is due to two main factors: (1) Most important... Infant mortality has gone down (2) Mothers dying in childbirth has gone down... there is also a small increase in folks surviving through pandemics because of anti-biotics. Looking at different scientific analysis of the data, if a sixty year old today lives any longer than one did at the turn of the LAST century is by NO MORE than a few years. Google myths, longevity infant mortality for more info...
You know, the last surviving soldier of the American Civil War died, I believe, in 1959. Some folks have always lived a long time. But in general, if you survive your first few years, you will likely live to see 70. I think that's been true for a long time.