The idea of retirement is literally thousands of years old at this point. Hell the Roman Empire even had the idea of pensions though it wasn’t that common at the time.

Aging inherently means being unable to be an independent productive member of society at some point. (Ed: well past what we consider retirement age.) Historically in agrarian societies few people reached this point so it wasn’t generally a significant burden to support them. What changed is lowering the retirement age and increased the number of people who live long enough to see it.