First he'll have to start a career in KART racing, though not strictly necessary.
When he's 16 he'll be old enough to start Car racing in Single Seaters (compared to 17/18 to drive on the road, at least as far as UK laws go)............ in a series such as FORMULA FORD, etc.
But before he can do that, he'll have to apply for a RACING LICENSE (which means going to a racing school + also having a medical).
After Formula Ford (or similar) the next route of progression is usually FORMULA 3... if he comes 1st or 2nd in the Championship (particularly a top one like the British F3 championship) he'll qualify for a SUPER RACING LICENCE which entitles him to race in Formula1 (if he can get a drive) + there's usually a prize of a test session in an F1 car.
After Formula3, the Drivers then traditionally progress further up the career ladder to GP2 (or "Formula 2" or "F3000"). If he completes a full season of that (without any mishaps that result in a ticking off from the race officials), he'll then qualify for the SUPER LICENCE needed to race in FORMULA1.
For more details, check out:
http://www.msauk.org/site/cms/contentviewarticle.asp?article=784
Current youngest ever F1 driver = Jaime Alguersuari (19)
http://en.wikipedia.org/wiki/Jaime_Alguersuari