I did my first paid contract when I was about your age.
It wasn't much money, but then it wasn't a terribly complicated project. It was probably technically illegal for me to do this, and some people might call it exploitation, but I didn't really care - it was fun to do and gave me more money in my pocket than the firewood chopping business I'd run when I was younger (not to mention much less hard work *8').
Then I got Vat registered when I was 16 and lots of people that I went to university with took a year out between A-Levels and first year of university (between 17 and 18) and spent that year (a gap-year in British English) working in an industrial placement. Some were lucky enough to get placements with IBM, others with Philips, others spent the time running their own business. One friends code, which she submitted as a patch for OS/2, was found still in the NT source code when it was released years later, it may even have made it into more recent versions of Windows.
There is a long history of talented young programmers making significant contributions to serious projects and with the current open source movement, that's easier than ever. Don't let your studies slip, but don't close off your options either. If nothing else, your experiences will give you nice anecdotes to reel off in interviews when you're 40. *8')