Don't buy what the Marines tell you. Finish college and then, if you still want, enlist.

The Marines can be a good career...FOR AN OFFICER! Your best bet is to ask the Marine recruiter what kind of college degrees they value in the Marines. Then major in that, graduate, THEN enlist in the Marines. If you like your career as an officer in the Marines, great. If not, you can go back to college at their expense and get another degree or go into the civilian working world with a degree + experience + military service. It would give you more choices. And while you are in college in preparation for your life in the Marine Corp and Basic Training, you can work out and take PE classes at your college to stay in shape.

Talking traditional parents into or out of anything is a job so hard it's never been done. It'll be simpler and more productive to keep your own dream of a military career and combine it with theirs. That can work out very well.

What was it about the Marines that struck a chord with You. Actually a lot of the military persons I know are in college as well or deferred enlistment until after college. Can you not finish your degree and then go in at a higher rank with the Marines. I'm not a Marine but maybe you could compromise with your parents in this way if you genuinely want to be a Marine.

I don't really have any advice. I just wanted to wish you the best. Good luck my friend.