Girls Puberty Dear BeingGirl Experts, What plays more of a part in when a girl gets her period —her environment or her genes? I ask because I am almost 14 years old and haven't gotten my period yet (or breasts) and I'm starting to wonder if I'll ever get it or ever need a bra! All of my friends have gotten theirs, so I'm wondering if the reason I haven't gotten mine is because I moved here only three years ago. L.A.S. --- Dear L.A.S., Physical maturation during girls puberty is mostly determined by the genes —in fact, you will probably start puberty or menstruating at the same age your mother was when she started. Environment can play a role too, though. The average age of menstruation is around 12½, but some girls do not start menstruation until they are 15 or 16 and this is totally normal! Try to enjoy this time of your life and not worry. Also, menstruation, breast development and many other things are a part of puberty for girls, and they happen at different times for different girls. You're right where you should be in your development. Hope this is helpful, Your BeingGirl Experts Questions about girls puberty? Get answers from the BeingGirl expert.