From my sister’s experience (so take it with a significant heap of salt) at the Air Force Academy:
It’s very much joining the military. In June, a week or so after she graduated high school, we dropped her off at the airport. She had a backpack with, if I recall correctly, some paperwork, some underwear, and nothing else. She spent that first night in Colorado at a stranger’s house - there are volunteers within the community who let incoming cadets crash the night before “in-processing”.
Over the summer, it’s basically typical military basic training. The first half of the summer they’re on-campus, getting an introduction to All Things Military. I know my sister went through some drill where they were all in their dorm, one of the upperclassmen in charge called out a uniform, and they had <some tiny amount of time> to change into that uniform and get back into the hallway. Of course, as with everything, even if you did it right you were still wrong.
For the second half of the summer, they march out to a camp in the woods, learn how to shoot, do obstacle courses, etc. There’s still lots of yelling and pushups and such, but there’s a light at the end of the tunnel. At the end of the summer they officially take the oath and become “real” cadets.
During the school year, in addition to a heavy courseload (the service academies lean very heavily towards applied sciences, by the way), they’re still limited in where they can go (including what parts of the walkways on campus they can use, just because), whether they can leave campus (not often), and what they can do on-campus (not too terribly much in terms of fun). They’re allowed only a few (5?) personal items visible in their room. It’s a very controlled environment - plenty of stereotypical college actions (drinking, sexing, making a 2 AM Taco Bell run) can get you in big trouble. I can ask about what happens when you do get in trouble, because I don’t think my sister did (she was too busy learning how to be a rocket scientist, and taking Russian at 7 AM). Overall, it’s an incredibly rigorous year, and I imagine your fictional young man can find himself struggling - almost all the cadets are used to being fairly large fish in a small pond, and now the pool is huge and full of sharks. He’ll likely work harder than he ever has (assuming he doesn’t flunk out).
At the end of their first year, at least at USAFA, they have a “recognition” ceremony. Basically, the upperclassmen put the freshman through hell for I think a full weekend, both physically and mentally (screaming, running them ragged, right back to everything you do being wrong, for two? full days). At the end of it, the freshmen get some bit of uniform insignia and are officially “recognized”.
Wikipedia has some pretty good stuff, and I know there are plenty of websites for concerned parents, which may be more helpful. If you want any specifics, I can ask my sister, but I can’t guarantee a prompt reply, as she’s now crazy busy learning how to be a test pilot. (Note: military academies seem to attract an interesting combination of ‘people who are there because Daddy is a general’, and ‘people who are there because they are absolutely compulsive hard workers and always need to be the absolute best’.)