[AnimalMuppet]

I've heard it described this way: In terms of physical health/conditioning/training, from 20 to 40, the question is how much can you get. From 40 to 60, the question is how long can you keep it. After 60, the question is how slowly can you lose it.

You may say, sure, I care about physical health, but why do I care about conditioning or training? Because when you're 30, conditioning is whether you can sprint or run marathons or play sports. When you're 80, it's whether you can walk without pain.

Note: By "conditioning" here, I don't mean that you have to reach 10% body fat or 20 inch biceps or elite VO2 levels or anything like that. I don't mean obsessive levels - those can cause injury and/or result in shorter life span. I mean, though, that you make some effort to work on your body's condition (strength, aerobic, or both) in a consistent, long-term way.