Well, if you're going to take advice from krazed and Rabbit then you should know every girl (especially younger ones) won't just bed you in a few days, assuming you will get her into the bed before you're 18, please make sure of a few things:
It's legal.
She won't claim rape.
You wear a condom.
You don't make a habit of it.
Alot of kids won't listen to reason and alot of times you can't reason with them, that said sometimes you have to just let them experiance it them selves.
Have fun man.