Dear Young Folk,
Physical aging happens ridiculously fast. Faster than you imagine. The years just tick away like minutes.
Mental aging goes much slower (barring dementia or other malidies, of course).
The crazy thing is that even once older (I'll turn 60 this year) your view of yourself quite often feels like you're still much younger.
I internally feel perpetually 30-35. Until I try to (say) run or sprint, or jump off something, then... oh my. I really am 60. Another example: my brain knows how to throw a fast ball (ingrained from when I was a teenager). If I actually try... uhh.. no go. My arm revolts.
I've even asked my 83 year old mom how her internal self feels. She says the same - still feels like she did in her 30s on the inside. On the outside she has to intentionally walk very carefully so as not to fall and break something.
Moral of the story? Enjoy that young body while you have it. Seriously. It won't last.