I have a good friend from high school who’s a career Marine officer (went to Annapolis). Brilliant guy, and believes the Marines is one of the best options for anyone who has the drive. (And he’s fervent and impassioned on that—last time I talked to him about it, he nearly sold me on believing that I should have gone that route, myself, and trust me, that’s not where I would ever hope to be.)
He also believes that someone drawn to the Marines who has the intelligence for it should be an officer. My friend will readily admit that there is, shall we say, a wide range of intellectual abilities among the Marines enlisted ranks—the stereotype of the dumb Marine is only a stereotype, but there are a good number that fit it.
But in order to lead such a disparate group, you need officers with top-notch intellectual abilities—and in my (limited, but not hugely limited) experience, the Marine officer ranks are largely populated by such absolutely brilliant people.
(Also, the quality of life for a junior grade officer is way better than quality of life for someone in the junior grade enlisted ranks. I mean, really, really way better.)
So: If the OP’s son really wants to use his talents in the Marines in ways that they’re most needed, he should look into becoming an officer in the Marines—and to do that, as has already been pointed out, he will have to have a four-year degree.
And obtaining a four-year degree while serving in the Marines enlisted ranks will be nearly impossible, and if he serves one tour as a Marine and then goes to college to earn a degree, the window for becoming an officer in the Marines will be rapidly approaching its close (since the age limit is 28).
Also: Lots of useful information at the [Marine Corps FAQ](Frequently Asked Questions (FAQ) | Marines) page and the [Marine Corps Officer Candidates School](Become a Marine Corps Officer | Marines) page.
(Note particularly the “paths to become an officer” link near the bottom of the page. The enlisted-to-officer path is long, and there are weed-out moments at every point along the way.)