Let's be honest: your twenties are probably the best years of your life. You're still young enough to enjoy life and your body still works, plus you've started working and maybe have a little bit of cash and independence, but not too many responsibilities yet.
That said, it's easy to miss the forest for the trees and spend that decade messing around and living too much in the moment. Some people who have seen their twenties come and go got on Reddit to weigh in on how they wished they'd lived life way back when.
1. A run-on sentence from Rusky82.
Exercise. Your body's metabolism will slow as you age and if your unfit it will just get worse. Put the effort in early.
2. Or ideally, ZuluCharlieRider, both.