Adulthood is an illusion, the world is run by big stupid kids with an agenda.
That said the world got a lot bigger after 9/11 for me. I was in middle school and the whole school day was taken over by the news coverage. I didn't know it at the time, but that was the point where doing things for the fun of it stopped being fun, where playing games and watching cartoons became more of a way to escape the seriousness of the world for even a short amount of time.
Everything else had a point and purpose, school was to prepare for college, college was preparation for a job, jobs were a means to get money to secure a house and food so I could hole up on my days off and forget the world around me.
Sorry if this was a bummer, I'll end on a favored quote of mine, "most adults didn't decide to grow up, they just got to a point where they couldn't stay children anymore."