That is something you have to be at peace with in yourself. To some people, if you're not living independently by the age of 19, you're not an adult. If you don't have a job, you're not an adult. If you don't have a family of your own, you're not an adult. What makes
you an adult in your own eyes can vary. I can see why you would feel this way because at least for me, I've never believed teenagers should be having sex. So to me, having sex (or not having sex)
is an adult's decision. Having sex does not make teenagers or anyone else an adult though. To me, what makes someone an adult is having integrity, to follow what they feel is right in all situations. It is being responsible for one's actions. If you can do those things and
not have sex, you are still an adult. Likewise, if you can do those things and have sex, you are still an adult. Again, your sexuality is
your own. The labels you give to it and to yourself matter a whole lot more than any that can ever be given to you by someone else because this involves a very intimate part of you -- including your intrinsic beliefs and morals. To me, you are an adult because you think as an adult. In your posts, I can see that you think things through before making any hasty decision.
That is something an adult does.