Help getting Parental consent?

I am 16 and have roughly 6 months before I can enlist in Marine DEP. (Not interested in early graduation) I believe the DEP would be most beneficial and if I get a full ride somewhere next year I can always get out...Not that I would want to it just gives some comfort to my parents. I am interested in combat photo, and I believe the experiences I would gain and the people I would meet as a Marine would help me to become a better civilian, I am not interested in becoming an officer even with better pay ect It's just not for me. Both my parents are very hesitant to sign with me mainly because they are afraid that I don't know what I want...things like that, how can I prove to them that I have made up my mind, and what can I do to persuade them to support my decision??