This isn't really a subject I'm qualified to write on, seeing as though I'm 19, I'm still at uni (and will be for a while yet) and have never really had a proper career or even anything approaching responsibility. There are tons of books about finding the right career or discovering your true passion. And I haven't read any of them either, so I can't comment on those.
But I saw this comment a while ago, and came across it again this morning, and I still think it's awesome advice.
From the Rudius Media Messageboard, a user called senorViper says:
"Go out, get drunk, get laid, study when its called for, and find your passion through living life. Then you chase it with everything you've got."
This is how I want to try and live my life.