The question that you should be asking is are you ready for the commitment and consequences associated with sex. Sex isn't just the act of having sexual intercourse. Sex is emotionally and physically binding. You and your girlfriend have to be aware that taking your relationship to the next level will also increase your level of responsibility. I am 28 years old and I have a five year old son. There will come a day when he too will be "ready" for sex. Here are the questions that I will ask him:
1) Are you prepared to support your girlfriend emotionally and whole heartedly?
2) Are you prepared to take the responsibility of protection on yourself?
3) Can you remain commited to her after you move forward and begin a sexual relationship.
4) Are you positive that this is what she wants.
Speaking from the female prospective, sex changes everything. Females become very attached to their partners after their frist sexual experience.
Speaking from the maternal prospective, protection is key and is the responsibility of both people involved. Birth control can only do so much and the male participant must protect himself as well.
Make sure that you are on the same page. Check and double check each others feelings and opinions on this. Talk to your parents if possible in a open conversation. They deserve to know how serious you are about your girlfriend and how much you two care for each other. This decision will change your life. For Good or Bad is up to you and how you handle yourself.