When my maternal grandfather retired, he retired from life. Spent his days in his favorite chair staring at the boob tube. Eventually, his muscles atrophied and he could barely move, let alone walk. His brain also atrophied. Nothing to challenge him and keep his brain active. He died at age 77 -- not young, but I wonder if he could have lived longer had he turned off the tv, got up and went walking at least.
By the way, his children took a lesson from him and remained active almost till the day they died.