There's an excellent MSNBC documentary on this very topic... details an ftm who lived as male from age 8 or so on, then started T around 13 or 14. He went through a lot to get T... most places, as I understand it, will only prescribe hormone blockers to halt puberty until you're 18. However, if your parents are on board with it, you may get lucky and find someone to prescribe you T.
I'm pretty certain there's no one on this site, however, who started T prior to age 18. Doesn't mean we can't try to help you though.
SD