I think it is human nature to question, especially at such a young age. Hell, I am 26 (I know, old balls) and I still question a lot. We have that fear of everything being so absolute, as if this is it, this is the best we can do and holy crap, I can never change this... it is a scary proposition.
Commitment is tough when you haven't even fully committed to yourself yet. It scares the hell out of people to be growing up; not only growing up but forced to grow up simply by economic and social pressures beyond your control. Life is crazy man, that's all I can say. We all are racing around trying to figure out exactly what it is our life has become; is becoming etc. and we sometimes forget who we are and what WE want to do.