A lot of the recent comments above concerning where the real education comes from is why I suggested going reserves/NG early on in this thread. Sorry for the short response then, that was my two minutes of scrolling the Hide before heading to bed so it didn't get a thorough answer. But, I got a little time now so I'll try to expand a good bit.
First and foremost, your boy will do what he wants, and as a parent, veteran, and former USMC recruiter, I highly encourage our education and nudging in a good direction of our young as well as taking a hands off and let them become a man choosing their own path. Good on you OP for trying to get some outside advice on how to guide him, and it sounds like you're taking the "trust in him" approach while trying to give him a good azimuth for him to follow. I was Marines, wife was Army, oldest step-son is active duty Navy, middle one is prior Army, and my teenage daughter is looking at military once she's old enough. We're very much a military family, and we know all too well both the pros and the cons with military service.
The military is far from a trade school, and is anything but a learning ground for an engineer short of civil engineering type work. They don't design a single thing, that's done by private industry, all they do is come up with specs to be followed and even that is 95% done by DoD civilians. For actual uniformed personnel, everything is user and maintenance level knowledge, and the majority of the time, especially when it comes to weapons, the users aren't the ones doing the maintenance other than basic preventative maintenance. I would highly discourage anyone from seeking out military service where their primary goal is understanding the core functioning of weaponry, instead it is understanding the usage and employment of weaponry. I hope I'm explaining the difference well enough there to be understood.
For anyone to be successful in military service, they need to understand the service side of it. The US gets more out of them than the service member gets out of the military. It's sacrificing of freedoms, the body, and the mind in many ways too. There's more rules and structure there than anywhere in free society. As much as it builds a man's body, it breaks it and leads to a lifetime of aching and pain. And with the mind, well, ignoring the mental effects of the latter mentioned, not to mention if there's combat service involved, is dramatic. That's why, even as a struggling recruiter during the height of the Iraq War, I would make sure anyone I took to MEPS was 100% on board with the knowledge they were entering into a world of sacrifice. Nobody, absolutely nobody, should join any branch for college money or trade learning as their #1 goal.
What young men and women get from the military, more than anything else, is the discipline and strength to succeed in life. It's not the only place one learn that, but it's certainly the top place outside good parenting. Even the best of us had some shit head traits when we were in our late teens and early twenties, and entering into that world of sacrifice and structure helps rid the mind of those. It's not perfect, there's definitely a 10% that never takes to it, but by and large those who are serving or are veterans gain it and keep it for life. I haven't been in uniform for 14 years, yet "who did you serve with" is one of the early questions when meeting anyone new because it has stuck with me and it shows without me ever trying.
But enough of my generalized ranting, here's why I say reserves for your boy. First, when joining the reserves, you're joining for a specific spot, MOS and location. There's no dream sheet or occupation field bullshit involved where the service gets to later choose how and where you serve, because you're joining for a specific MOS at a specifically based location. That even includes Marine Corps, the worst offenders of the "needs of service" mantra for active duty personnel. He would join the service, go through all the training, and then be assigned to a unit to be utilized as necessary. Reserve and NG units get a shit ton of schooling opportunities to advance one's career, most of which go unfilled because everyone is too busy with their regular life to bother going to the schools. I've known several who got out and went reserves just to get school opportunities like jump, dive, Sniper, SERE and Ranger, then return to active duty schooled out and running with the big dogs. Once he's on the reserve side of things doing his one weekend a month, he can pursue education or craft he wants.
Almost every single job filled by active duty is also found in the reserves. SOCOM wise there's even 19th and 20th SFG as well as ST 17 and 18. PJs, CCTs, TACP, and USMC Recon are all found in the reserves. Yes, it's very competitive to get into those units, not being in a rush is a big advantage.
Finally, I absolutely discourage going "armorer" in any branch if one wants to learn weaponry. Basic wrench turner is all it is. Even the USMC 2112 is nowhere near what it used to be.
Good luck to your boy in whatever he chooses. He sounds like a very fine lad and citizen.
I do Maritime law Enforcement(My rating(our job codes) is ME) As far as quality of life in the CG....lets just say I've met MANY more prior service branch(All were Army, Navy and Marines) guys and gals that have lateraled over to the red headed-puddle pirate side of the military than those who want to switch over to a different branch. I've never met someone who wanted to switch out of the CG to a different branch. They all come over to us. That should speak volumes in itself.....
