The Marine Corps recruits HARD among very young kids. Most recruits are 18, unlike in the Army and Navy where the average age is about 21. Personally, I think 21 year olds do better in the military, but the Marines have their own (very young) culture.
The GI Bill is a very good deal. A lot of people literally could not afford college on their own. The Marines do not offer the Student Loan Repayment option. Most college campuses do NOT have ROTC. And most people max out on their loans and STILL have a large portion of a tuition bill left over. This leaves them with two options: drop out or take on punishing private loans which do not have the same protections and repayment options as Federal loans. I would counsel anybody in that position to drop out. The debt is not worth it.
I was fortunate in that between a scholarship which covered 25% of my tuition, and and Federal loans, I was able to get through college without paying much out of pocket. I graduated from college at 21. Then I enlisted in the Army, which has a lot more money to throw around than the Marines - they repaid my student loans in full over my first three years of service. Now I'm using the GI Bill for grad school.
My suggestion to you would be to look into a different university. There are statistics available on what percentage of the student body is "non-traditional." My university is a good one in that regard, it's the "city branch" of our State University system. Unlike the State universities out in small towns in the periphery, our branch of university is in the city center, in a working class neighborhood. Nearly half the students are working adults, or have come back to college after several years as working adults. We have a strong "adult student" community that meets regularly. Many students are in the their forties, a few in their fifties. In fact, tuition is FREE for students over sixty.
I STILL felt like a space alien the first few months on campus. But I've largely adjusted now, thanks in large part to my fellow adult student. In one of my classes, four of us who sat in the back formed a group, and we collaborated together on all our labs and assignments. Our professor encouraged it, she said as long as we passed our exams independently, everything else could be a group effort. My group consisted of a 50 something Navy reservist who was working full time, a 40 something professional (works for our city water system), a 20 something year old "traditional student," and myself, a six year Army Veteran. Since we were all fairly mature and had spent enough time in the real world to get over ourselves, this worked out great. We had a good time, learned a lot, and I credit them with my adjustment to college life. (And helping me with the math!)
I think it also helps that I am now in the National Guard, so I get to hang out with other Vets one weekend a month. We spend some of that time #itching about civilians, I'm not gonna lie.

And there's a fair number of "former" Marines in my unit too - you'd be welcome in a Guard unit. Of course the Marines are always making fun of us, and vice versa, but they're a really accepted.
If you can't find some fellow Vets or "grown adults" to hang out with, I suggest you look into transferring to a less traditional campus. I wish you the best. Keep venting, and find a real human to vent to, it sounds like you could use a sounding board. And join the guys over at communityofveterans.org if you haven't already. Good group of guys.