It really depends how much younger than 18 you are, how mature you are, and what the people ar elike that you hang out with...
Game in highschool never usually bodes too well, but when you're outside of school, you can run game as if you were 18, opening girls your own age.
The beautiful thing at this age is that unless the hot girls are with someone, they are only ever used to complete douches, or complete pushovers...which is why they go for older men (who take on some of this stuff naturally with age.)
If you show them you're not like other guys out there (people she's dated) she will take a very big likeing to you and you'll love it, cause word spreads and girls will hear only good things about you.
Every girl I have gamed since getting into the community will say with confident, and tell me on a regular basis that I'm not like any other guy they've met. I'm almost like an 18 year old...
I have a HB10 (This girl is really mature for her age) who wants to lose it to me, cause she thinks I'm perfect...And on saturday I went mall sargin to see what it was like and to get over AA...I opened 3 sets (just to get the feel of opening) and then got a 20 year olds number within 20minutes (Granted she thought I was 18, but hey :P)
I'm not blowing my own horn here guys...I'm just here to show you it's possible! Just cause you're in school doesn't mean you can't game! Get out there and put your ego on the line, cause it'll blow up like crazy once you do it enough
But I'm a little scattered at the moment, I will be updating this regularily.