Your body is the only thing that, the more you use it, the better it gets. Can you imagine if cars were like that? You'd start off with a Dodge Dart and eventually you'd be driving around in a Ferrari.
Author's father.
I have people in my life that I can use as bellweathers of what I should keep in mind as I age. When I ask these people about what's important to someone as they aged, a common theme is "exercise".
I don't really care how you get it done. What matter is that you get regular exercise. No one ever regrets getting enough exercise. And as you get older, the positive impact is magnified.