Leaving the marine DEP for other branch?

I broke my arm and had surgery about a month ago.during my down time i realized i wanted to serve in the air force. i told my recruiter that i wanted to be discharged from the DEP program. they then told me that it would be 6 months before i would be discharged and that i should reconsider my decision. after i left they said that they were going to medical discharge me and i should find out weather my having surgery the air force would even accept me. can they do this and if so what can i do either stop it or insure me getting in to the air force without the medical discharge?