It takes multiple generations for this to cause an impact. What matters isn't the people living longer who are born today - it's the ones living longer who were

It takes multiple generations for this to cause an impact. What matters isn't the people living longer who are born today - it's the ones living longer who were born in the 1950s-1970s. And it's taken additional decades for most of the poorer countries to catch up to the "first world", in terms of birth rates and lifespans. Consider, say, Iran. In 1980, its birthrate was around 6. Now, it's 1.4, lower than Europe, and lifespans shot up at the same time - but only for those born during the health revolution there. So those people are still less than 40 years old. Iran is just now starting to feel the impact of increased lifespans, and it'll take another 50 years for that to truly stabilize.