Hello, I'm a MTF, and I guess we are the same age, and I go to high school just in case, so I understand how you feel, about transitioning, my family isn't supportive neither they are muslim they will just kill me, so you have to be strong, finish high school, and apply for college in a different area from where you are! So that you can be independent and you whatever you want and then transition!
You cans till make some little changes, like cutting your hair maybe (?) I mean if they don't want you to, you can still do it by yourself I guess, or just go somewhere alone, after you did it, they can't make it grow right away so it's something already, then you can start buy masculine clothes, and change at school, I want to do that next year, since my sister graduates and she is not going to be in my same school, I can be more free there too, so that people won't tell her, and stuff...You can like work out I guess, just to prepare for you transition that will happen when you can be independent!