Perhaps a Marine here can fill me in. In the Army, you don't re-enlist after an enlistment that carries you past 10 years of service. Is it the same in the Marines? If so, this is a young SGM.
I'm no authority on USMC, (being retired USAF), but believe the Marines re-enlist upon expiration of term of service, similar to the Air Force. The Sgt. Maj. was probably going over 20 on that reenlistment.