(1) Are you planning on going to university? a) most top (u.s.) universities look down upon graduating early. They'd prefer to see you really use up all your resources in your area and say, win siemens, start a non-profit, become a lobbyist, start a start-up than graduate early. b) can you get into a (good) university right now?

(2) Finances. Do you currently rely on your parents' finances? Upon graduating high school, will this change? Would you have to pay for university yourself?

(3) Are you mature enough to be doin' what 18 year olds do when you're 17? I assume you're a dude (most folks here are), and dudes mature slower than girls do. There's a big difference between 17 and 18 (although not really a big difference between 22 and 23, or 40 and 41...)

(4) (small one) Having to explain to all your peers for the next 5 years that yes, you are younger than them and why. Not being able to drink in public legally for a year longer than all your friends.

Honestly, I don't know where you live, but I'd look into Other Enrichment opportunities before graduating early. I went to a state-run public boarding school for science and math in my junior year that was more like college than some colleges are. Can you just take less classes senior year and work on a start-up? (I presume you're interested in those 'cause you're here...) Are there good universities (or bad ones) in the area that you could take classes at?

All of those seem like much better options than graduating early and "starting life" earlier. "Starting life" always seems just around the corner when you finish yet another milestone, but I'm slowly becoming more aware of the fact that life starts now (not to get too philosophical).