If you are interested in applying you should make arrangements for a briefing at admissions. You'll get onto the campus, and likely get a tour with a cadet. When we did it the whole family was able to sit in on the briefing.
After that you'll be able to roam most of the campus at your leisure.
You'll need to check, but I'm pretty sure they allowed Sophomores. Juniors for sure.
You'll need to plan your visit to fit their hours, but it's more fun than the commercial tour, and you'll see more. The tour is good, but you only stop at trophy point and the chapel on most. They do cover quite a bit of history, etc.
If on the weekend, you can attend church at most of the services. You can also eat at the Thayer. Both give you a reason to go on campus if you can't arrange an admissions briefing.
Once on the campus there are some natural walking loops, you leave your car at Buffalo Soldier field near the S Gate & Thayer. There is also a shuttle that will carry you if you are in a hurry. After walking you can drive over to Ike hall, etc to see some of the areas that might be a bit far to walk.
While it's mostly an open post we've been told, security does want to know your reason for visiting and you'll have to have your vehicle inspected. Photo ID for all over 16. They may ask for insurance & registration.
Hit the museum & visitor center while you are there. Both are free. The museum is worth a visit.