At 17, self-selecting hobbies are a decent start to start weeding down to guys that could possibly be gay and just aren't out or in tune with it yet.
So, think about what recreation or hobbies sound really interesting if your biggest motivation is being around and being close to other men. Like what interests involve giving up time chasing girls in favor of spending time with the guys.
This can be a mixed bag, as some all-guy things like sports give guys better status with women and that's one of the motivations for doing them.
So, school-sponsored wrestling? Probably mostly straight guys. Private jiu-jitsu club run out of a guy's house? Probably some bi or gay interest showing up in some of the guys there.
On the other side of things, interests that mostly only appeal to guys who are comfortable enough with their sexuality or not worried about being seen as gay to do them. Some of these can be stereotypical things like theater, but others can be sensitive guy interests like avant garde music or art. That still won't be all gay, but you'll have more guys with fluid sexuality in the mix.
In general, if you're gay, and you pursue interests that appeal to you, there's a good chance that another gay guy who's similar will eventually show up.
Overall though, I think the easier way to read guys isn't by how much they're motivated toward men since a lot of guys will still hide that at 17. Instead, you know more by how motivated they are toward women. Not like the guys that just say it, but the guys that are cutting out time with other guys or making sacrifices to their time and wallet to be with women. The guys who aren't putting any effort that way are more likely to be gay if they aren't just terrified of women. But, even the guys terrified of women will still go to some lengths to find one.
So, look for the guys that really like the all-male dorm and are first back to hang with the bros at curfew or the guys overly obsessed with weightlifting mags. Some of those things will lead you to guys who like guys eventually.