One of my friends says she's done it only about 4 times, and another one says she doesn't, and a third says all girls do it. What is the percentage of 13- and 14-year-old females who masturbate?
I have no idea. But it's safe to say certainly not every girl your age masturbates. If one of your friends told you that, we have to say to you, don't believe everything your friends tell you! Surely some younger teen girls masturbate regularly, but I'd have to guess that among the general population, the fraction is probably one-third or less. Many women discover masturbation when they're a bit older – 16, 18, 20, and beyond.