My body feels even better than it did when I was in youth.

At twenty you could sleep on a friend's floor and feel nothing about it the next day. That was mostly luck, and mostly ignorance.

What youth had was the ability not to think about the subject at all.

What comes later is information. You know which shoes ruin a day, how much sleep is the real number rather than the number you claim, which week is difficult and roughly why.

None of that was available to the twenty-year-old, who couldn't have used it anyway. Feeling better isn't only a matter of capacity. Some of it is no longer being at war with equipment you don't understand.