What size do you think my penis might grow to and when will it stop growing?

Hi my name is Mike and I am turning 15 in January 2018 and my penis size is around 7 inches. I really am anxious about my size and I feel like it wont grow at all so I want to know when it will stop growing and what size it might be by the time i'm either 18 or 20, thanks. 

- More info: I am 5'10 and my girlfriend is 4'11 and she thinks its too big for her and I think so too but what do you think would be the right age for sex? We both think 15 would be right for us and I just want to make sure i'm not doing it too early.