You're sickeningly young (from the point of view of someone who's 31 soon), and you have all the time in the world.
Heck, even I still have a twinkle of hope of making something worthwhile out of my life.
At any given moment in time, just do what you feel like doing - especially in your case, where anything you feel like doing is likely to be productive/useful anyway.
As others have quoted all kinds of important people too, here's mine:
"Don't worry - be happy" (Bobby McFerrin)
:)