Best Friend with a Girl ?

I have a very close friend and we known each for a little over a year now....shes closer to me then any other of my friends plus most of them bounced after high school but shes stuck around....we spend nights talkin,texting,IMing,facebook chat ect.....we have so muh in common and basically havethe same personallity...i never pulled any moves on her and we have a perfect friendship....i'm wondering how long this is going to keep up because i may want to date her later on but i don't wanna mess this perfect friendship....i'm 19 and shes 18