“Well, back then you were considered an old man at 50” and other half-truths

Thanks to oversimplification and societal innumeracy, it is common to hear this from people of every educational level. A related illusion has to do with how much longer people are living these days. This one has a modicum of truth but is, IMHO,exaggerated. The main difficulty arises when we use average life expectancy AT BIRTH as the jumping off place. While it is true that in 1910 the average life expectancy at birth for white males was only around 50 years old, the reason had to do with the still high infant and child mortality rates that dragged down the average death age. In fact, after a person attained adulthood, the numbers change dramatically. The average life expectancy of a 40 year old in 1910 was another 27 years (average death at 67). A 50 year old would die, on average, at the age of 70; a 60 year old could expect to live to 74. These same age groups today would expect to die, respectively at 79, 81, and 83. While these numbers are significantly higher, they represent a much smaller increase than the life expectancy at birth in 1910 (50) and the life expectancy at birth in 2003 (75.4). In fact, as one would expect, these differences converge as the population group under question is older. An 80 year old in 1910 could expect to live another 5 years. An 80 year old in 2003 could expect to live another 8 years, a difference of only 3 years. In fact, even in the middle of the 19th century, it would not be correct to state that a man of 50 would be considered old even though the average life expectancy at birth at the time was less than 40 years! We are seeing a tremendous number of older people these days but it has more to do with shifting demographics than it does a drastic increase in the adult life span. Anyway, this is my understanding using figures at hand: http://www.infoplease.com/ipa/A0005140.html
I’m willing to be proven wrong. What’s surprising is how much we rely on the “at birth” figures when they’re usually irrelevant in discussing our aging population.