naturally, ur parents are gonna oppose. every inkling of ur existence,
they gave u. but what they don't see is that U have to use WHAT THEY GAVE U...
ACCORDINGLY to how u have developed as an individual and as a human being. u will continue to develop...and a lot of other outside influences are gonna mold u. try to focus and see the big picture.
first and foremost, u need to do a little research to see what the marines are all about...if that is what u are interested in. talk to people who have served and/or serving. once u know what ur getting into...AND if u are still sure after solidifying ur knowledge about it, u must help ur parents understand also.
believe it or not, ur parents are gonna be ur biggest challenge right now. if u can get pass them, and compromise with them, the only thing left to deal with is U and how u want to direct ur path. a lot of ur parents' reaction is coming from the media, i can guarantee it (i.e., television, radio, newspaper, etc....and actually, even their own personal experiences). those types of provocation comes from the depiction of war as it is deplored into society. however, that doesn't necessarily mean it is something that u will be inhibiited into. everyone is different, everthing is different, every nation will be different...and so forth! show them the difference in u, and how u will deal with those "things", those "people", and those "places". let them know that who they raise will make decisions comparable to who they are. u can't deny that a lot of who they are is who u are, vice versa.
of course, ur parents will forever see u as their baby, we all know that...cuz u ARE their baby...but if they understand what u are getting into and understand who u are, they will at least compromise with u. the wonder will be how much u can bring back to them...in U, who u will have become...and the being which they created. this shouldn't be a problem if u focus. from what i've read in ur statement, u just want to give urself more options...it's not just that u don't want to go to school. that's good. ur thinnking reasonably. just don't forget to research. and don't let anyone tell u that u don't know what ur doing, or that ur young and stupid...especially if u feel right about this. because u know urself better than anyone.
good luck, and i wish u well.