I didn't know.
I was raised by hard-core career academics and was merely certain that i didn't want to do that.
I flunked out of programming classes in highschool attempting to see if i could be a programmer like my oldest brother.
If i'd been raised by steel workers I'd be the sharpest mechanic at some automotive shop, and perhaps happier than i am now. But i was raised by people with advanced degrees in the humanities and it didn't occur to me until too late that maybe it's ok to just learn a trade and do the work.
At any rate, I don't recall having a specific aspiration. I mean, sure, i wished i could make money as an artist or something, but i was too cynical to go through with that.
I have a friend who followed that career track. He works for ebay, in customer service, and he's just lucky he married money. I'm sure he had a great time in college, though. I didn't go to college.
As it turns out, I break software for a living. my name tags say "Sr. Software QA Engineer" these days. It's boring, but i'm reasonably good at it and i can stop thinking about it when i get home at the end of the day.