I know there is some sort of loophole for military controllers to get past the age 31 rule but I'm not sure about the specifics. I was thinking it was only for Retired military personnel, and there are some restrictions on facility of preference, but again I'm not sure.
I will say I think you've made a fine choice with ATC in the Marine Corps. I work with Military ATC veterans every day from all branches of the Armed Forces, and the Marine Corps always stands out as the best. The Marine controllers seem to be the only ones who consistently know what they're doing, without exception.
Thanks for your service brother, and Semper Fi!