Am I ready?

My boyfriend is away for another month for military training and when he comes back we will have been together for about 8 months. I am a virgin and he isn’t. We have talked about having sex when he comes back and he isn’t pressuring me at all, he is waiting until I am ready. When he comes back I will be 17 and I am and will be on birth control. I feel like I am ready and I know that there are low chances of getting pregnant while on birth control and using a condom, but I don’t know exactly how high those chances are and I don’t want a kid at this age. Should I wait? If yes, how long? I don’t want kids until I am at least 21, would I be taking a big risk if I had sex before then?