They probably are immature, tbh. I realize I was being a little judgmental in my initial comment, sorry for that; I realize that boys and girls tend to feel awkward around each other--but it doesn't have to be that way! Do you have friends who are girls, or are you just trying to talk to girls as potential romantic interests? I was part of a large mixed gender friend group in middle school and high school and I think it helped me to understand how to communicate with everybody on equal footing regardless of gender, and that made it easier once I was actually ready to pursue boys romantically.