Easy, people were more fit and the cost of care was way down. They also didn't have the technology to "prolong" life. IMO the reason insurance is so expensive is because so much money is spent on trying to keep the elderly alive. Sure everyone wants grandma to live forever. However those treatments are expensive. This is a huge issue that no one ever talks about for obvious reasons. It's certainly a taboo subject.
plus there was no obesity epidemic, food was probably more pure too, no so much chemicals and hormones, we really are F__ed up today