I remember lots of stories of people selling things on ebay at a young age back in the day. I'm pretty sure some must have made more than $1MM in revenue.

Recently there was a story about a 16 y/o who's converting a sports car to electric and runs a CAD business that seems to be doing pretty well.

Edit: I just dug up the car conversion thread I mentioned. This kid is making amazing progress: http://www.s2ki.com/s2000/topic/975497-wait-that-isnt-an-f20... (that's the last page of his forum updates)