I know how you feel. I've always been a really petite and slender girl. I have people tell me all the time that I don't look my age. I've been carded a few times at the movies as well. I used to hate that, but now I've come to appreciate it. Just wait until you get older and still look 10 years younger. As far as whether or not you develop more, don't worry so much about that. When you meet the right girl for you, she will love you for who you are, regardless of size.