Hi goddess, have you asked your school if they'll allow it? Will you have to cover it? I only ask because if you play too much with piercings, especially the nose, they can get manky and/or never really heal. If they aren't going to accept it, it may be worth waiting (I know that's just annoying advice, and that you probably really want it now, RIGHT NOW, like I did!)
If they do, and you definitely want it, by all means go for it. Piercings can be taken out if necessary, and so aren't entirely permanent. I would still say though that if you are going to be in situations where you will have to continuously take out and put in your nose piercing, that is going to do it no good!
I was finally allowed my nose pierced, after years of asking, at 16, and after the right side refused to heal, I took it out and got the left side pierced instead-that also failed! This isn't a universal experience, it's just mine-I don't think my body took too well to piercings (my ears were often a bit skanky too).
I hope you decide what's right for you, independently of other people's opinions etc.