I really did want to be an astronaut, when I was about 6. Before that I wanted to be a jockey for a while, but decided that was out, on the logical basis that I couldn't ride a horse. It never occured to me, it seems that I could learn. (Later, much, much, later I did, and discovered I'd never have had the courage for racing anyway)
The thing that worried me about being an astronaut though, was the G force on takeoff - in the Tintin book, it made them all pass out. I can;t remember what I decided on after that, but by the time I was doing O levels, I'd decided on being a vet, but A levels proved to be too big a jump, dedication and result wise. Currently, I'm sort of an archaeologist, but only on paper, and sort of an editorial assistant, since that's what I actually earn money at.
I'm still hoping one day I'll really know what I want to be when I grow up. At nearly 40, I'm running out of time.