What Should I Do?

I am thirty-six and divorced, and a few months ago I had the opportunity to have a bisexual fling with a young woman in my building. I will admit that I have long been curious about being with another female.
Well, with Beth I was not disappointed. I found female sex to be very exciting as well as satisfying and see hy this has been becoming such a trendy thing.
The only problem is that Beth is quite petite. She’s only five foot tall and thin and is twenty-four years old, she looks like she is about fourteen. She is a nurse and yes, I have seen her identification. So she really is twenty-four. But she just looks so youthful and the fact that she flat chested and shaves down there and is smooth really does make her look prepubescent.
I really do enjoy her company and we go naked all the time at each other’s apartment and feel so free and uninhibited with each other. Still, the fact that she looks so youthful does continue to make me feel nervous. Like I am this mature woman taking advantage of this very young girl, especially when we are having sex.
The sex with her is great and obviously she knows what she is doing. She has told me that she enjoys being bi, although this is something that she has to keep a secret because of both work and her mother, who is very anti-homosexual. So because of this I do not feel at all pressured to be more open about my situation, and that has worked out nicely for me.
Still, the matter of my feeling like I’m with this very young girl does make me nervous. Should I just be relaxed about this and enjoy it, since it’s safe that I can obviously. Or should I perhaps choose someone closer to my own age? I am in a bit of a quandary.