In Israel at least there are probably hundreds (out of a population of 8,000,000) of programmers working professionally below the age of 18. They don't get on-the-job training, though, it's just so easy to teach yourself at home or in high school.

When I was 17 I started a program connecting high tech firms to winners of a programming competition for high schoolers that is still going, 14 years later :-) But I was far from the first to do this here.