can a teenage girl enjoy sex with an adult man? she doesn't want to give me any feedback

But why do you need to know from her if she is enjoying it or not. She may be shy and hesitant. With time she will get confident enough to tell you. You are a man she is a girl still so she must be a bit shy. 

You should be able to tell from how she responds and behaves when you have sex with her, if she is enjoying sex or not. Her facial expressions, her eyes, the flush on her skin, her moaning, how she opens her legs for you, how she moves her hips up and down when you make her orgasm, how she hugs you and kisses you. All those things are signs she is really enjoying it. If when you arouse her, she gets really wet and moist in her vagina is a really good sign that she is hugely turned on and enjoying the experience. 

I wouldn't worry about her not telling you or saying it out in words that she is enjoying the sex. Just watch her, observe her, study her responses, get to know her better and what she likes and turns her on. 

I was 13ish when I have my very first sexual experience with a much older guy. He was a fully grown man while I was extremely scared, shy and nervous at first, I slowly became more confident to be able to discuss sex with him. I really enjoyed my first time and he made it really special for me.  

it is over a year ago you asked this question. Have you got your answer? Are you guys still together? Does she still enjoy your company and has the relationship grown stronger?