I’m a vet of Iraq and Afghanistan, so maybe I can set your mind at ease a bit. (Although I was in the Army, not the Marines, so ymmv slightly.)
What is your concern, exactly? That you’ll miss him, or that he won’t be able to hack it?
If it’s the first, I totally get it. It’s tough, especially if he’s posted far away. That said, he has to leave the nest at some point. You should be proud you raised a son who has the initiative and guts to do something “big” instead of just living in your basement till he’s 40. He’ll see the world and broaden his horizons in ways that most young men his age never do. I’ve been in something like 20 foreign countries, some of them pretty exotic. It wasn’t always fun, but it was a huge part of my personal growth. I say this gently, but you can’t treat him as a baby anymore, or as your precious little angel. He’s a man now. You should want him to grow into a confident, well rounded gentleman, not stay trapped as a little boy forever.
If you’re afraid he won’t be able to hack it, I wouldn’t worry too much. Contrary to what you might imagine from movies, not everyone enters the military as some kind of He-Man Alpha male. The military is huge and contains all kinds of people. There are plenty of “nerdy” guys who enjoy playing video games who still get the job done. Perhaps he feels the Marine Corps will help him develop self-respect as a man. And don’t worry about him not being able to cut it. The Marine Corps is very good at turning civilians into Marines. They do it with thousands of kids a year. As long as he gets in decent physical shape and tries to maintain a positive attitude, he will be fine.
And also, what’s wrong with playing video games? I have like 13 years of military experience, and I still like playing video games on occasion.
Good luck. If you have any questions, I can try to help, although as I said, my service was not in the Marines specifically.