Well, if his wikipedia article is to be believed, he started off by selling games for the Atari and Commodore 64 (at the time using games to sell floppy discs). He obviously learned a little about programming and designed his first game, which was text based. (It sold two copies, and he suspected on was purchased by his mother).
Then moved on to bigger and better things as his skills improved and creativity flourished. You often have to start small. You don't just do a university course in computing and get an instant pass working for the developer of your choice.
Nobody ever gets anywhere on ideas alone, you have to make them real somehow. You don't become a a successful filmmaker without ever touching a camera and you don't become a novelist by never writing a word. You can become a successful musician whilst having next to no talent, but that's a whole other kettle of fish.
![Hmm [^o)]](/emoticons/emotion-40.gif)
The only thing worse than beating a dead horse is betting on one.