Well at 12 years old, you'll be living with them for awhile yet, so you might really have your work cut out for you because even if you start with a tiny hatchling now, it'll be 4-5 feet long by the time you move out. Just try to convince them that you'll be responsible with it... I ran into a similar situation when I got mine, and I still run into it with friends that are afraid of snakes. The thing that works for me is just to get them in the same room with one, have it under control, and they'll usually see that there's nothing to be afraid of. For some reason, all the people I meet that are afraid to be around my snake seem to be under the impression that as soon as they walk through the door, I'm going to get it out and throw it at them just to freak them out. I've turned a few people onto snakes using something like what I mentioned above, so it's worth a shot.
And also, if you really are 12 years old, thank you for not talking like one. Some people on here that are much older than you don't seem to be able to type replies without using chat room slang and without abbreviating every other word. Between that and the fact that you've done research shows that you're already respectable, so keep it up and that'll get you far with this crowd here. Even if you can't get the snake, stick around and learn - there are other people that post here regularly that don't have snakes, and you can never be too prepared for when you actually do get one.