Hi, Jake. I see from your first post that you are MTF.
You definitely need to tell someone as soon as possible, so that you can get on androgen blockers to prevent any further masculinization. It is not likely that you can get full HRT until you are 18, because of the permanent changes that HRT produces. But normal treatment for minors uses blockers to prevent any more development in the wrong direction.
How do you tell people? Well, I know it is hard (we've all been there), but there is only one way: just say it. If saying it face-to-face is too hard, you could write a letter. Pick whomever you think will be most sympathetic. In a perfect world, it would be one or both of your parents, but the world is far from perfect, so you may find it easier to tell someone else first. Do you have a counsellor at school that you could talk to? Your doctor? A good friend? The first one is the hardest; after that, it gets easier. Whoever you tell first, the objective is to get your parents in on the conversation, because they will have to authorize your treatment.
Sometimes parents are not sympathetic. If that happens, don't panic. You only have to hang on for a few years until you are legally an adult and can begin treatment without permission. While starting young definitely gives better results, there are many of us who only figured this stuff out in much later years and still transition successfully. I was 61 when I started!!
Like I said, I know that getting those first words out is really hard. It took me many months from the time I decided I needed to tell my wife until the time I could actually do it. Just keep trying until the words come out.
