Birth Control for Teenagers: Age Limits, Costs & Effectiveness

Question
A I'm 20 years old and I'm currently sexually active with my girlfriend who is 16 years old.  We have been together for more than a a year, we've been having unprotected sex for about six months now, she hasn't gotten pregnant, and we want to avoid that.  One of the questions that I have is..is there an age limition for taking Birth control such as the pill or the patch?  what are the prices for BC and if she takes the birth control will she continue to have her period?

Answer
You need to get birth control ASAP. Visit a local planned parenthood - she can get birth control for free there. She will still have a period when on the pill - but her periods may become more regular.
Please use condomds everytime you have sex! What you are doing right now puts you at a very high risk for pregnancy!
Dianna