I guess I didn't know what I wanted until I was in my late teens. Since then, if I have something I want to achieve, I'll go for it. Though I'm still chasing my dreams, as opposed to 'living' the dream.
As I get older, the more I want to do, so as not to waste my life being idel. Maybe it's the fear of getting older and looking back with regrets?! I don't know really. Something like that nags at the back of my mind.