My own observation is that a lot of decline happens because people stop living and start coasting to the grave, and that can happen decades earlier than 70. My

My own observation is that a lot of decline happens because people stop living and start coasting to the grave, and that can happen decades earlier than 70. My great-grandfather was physically very active into his 90s, still running his businesses, working in his orchards, and generally being surprisingly productive. He was mentally sharp too; I remember him teaching me about the physics of vacuum energy at length. Seemed like he could go on indefinitely. Then his wife died and he died less than a year later. I always have him as my model for what I want to be like when I am old. He was still in the game until he wasn’t.