Why do my brothers act like this?

Im a fourteen year old girl with three overly over protective big brothers ages 21,19 and 16. They are sooo overprotective it isnt even funny. They always treat me like im some little two year old who needs there help with everthing. It really sucks because my parents think they are right and I do need them. Im not even aloud to stay home alone. I have to have one of my brothers babysit me. I mean im fourteen and I still need to have one of my big brothers babysit me. I cant dress any way my brothers dont approve of and the answer to anything with the word boy in it is no. I sware if it was up to my brothers id still be in diapers. My parents dont even care about any of this when I tried to talk to them and explain that I dont need them to take care of me all the time they didnt even really listen. When I look back to when I was little it really seems more like my brothers raised me. I love my brothers but I really need them to see that im not a baby any more even though they see me as there little baby sister. How can I finally get it through to them that im a teenager and need my space. They wont listen to reasoning when I talk to them because they still see me as a little kid. I hate how they are always treating me like im young enough to be in diapers! What can I do?