It’s less about life expectancy and more about the ability to work. Many physical ly demanding jobs are pretty much impossible even in your early sixties. And at 70, many people are not mentally capable for a job much more demanding than a Walmart greeter.
Plus, most of the gains in life expectancy come from reductions in infant mortality. Actual human lifespan has barely changed at all. In all likelihood, your person who died at 80 in 1940 would probably live to be 80.5 today, and that extra six months would be enduring the hell of chemotherapy while the medical industry drains his kids’ inheritance.
While it is true that improvements in infant and childhood mortality were responsible for raising the life expectancy averages beyond age 40 in the past, more recently life expectancy has improved across all age groups. See here for some interesting details.