24 here, yet I went through a strange quarter-life crisis back when I was 18 so I don't feel too old yet.

I've learned that, at least personally, the more you sit around and do more or less nothing, the older you'll feel due to the world seemingly zipping by you at high speed. Going out and remaining active, doing whatever you can to keep that fire burning, and you can feel young for a very long time... at least until your back gives out or you're in need of a hip replacement.