When should I ask her to be my girlfriend ?

First things first, were both juniors in high school. I ve been friends with this girl for about a month and a half. I didn t start talking and getting to know her until 3 weeks ago. We get along very well, we make each other laugh, happy, and feel comfortable around each other. We work together but we go to different schools. We see each other to hang out and have dates about 4 times a week. We went to prom together and had lots of fun. I really like this girl and she really likes me. We kiss, hold hands, and things that a couple in a relationship would do besides sex. We re both really interested in each other. The thing is, I don t want to rush things too fast but I also don t want to be too slow. When should I ask her to be my girlfriend ? I ve heard people say 3 months, half a year, and up to a year. ecwrything seems to be going extremely well and I don t want to make a move too fast.