I don't think you understand his situation. He can attend a school like University of Texas for free and get paid a housing allowance. And yes the GI bill expries 15 years after seperation. Why waste such a valluable asset. Finish school now. He served 4 years in the Marine Corps. He is ready for school. He has all the maturity he needs.
Definitely the best course. He sounds bored and thinks working on a rig will change things up for him but the work is quite dangerous and you can't lead a normal life due to the schedule. I would apply to a great school and let them challenge you.
If it were my ideal choice, I would have joined a private contracting company long ago (blackwater before it became triple canopy) but there's too many guys like me with trigger time. Like I said I have a month to decide, I could always try it for a while then go back to school, but I'm hesitant to go that route cause I'd be afraid I wouldn't want to go back to school. I already started as a 24 year old freshman as it is.