Have you talked to a recruiter at all?
Making a 97 on the practice ASVAB is great, but you need to take the real one. You should meet the Air Force qualifications for a controller with that, but you need to talk to a recruiter to be sure.
MEPS is just screening to make sure you are fit for military service, as long as there's nothing to disqualify you for ATC duty, you don't have anything to worry about. You can probably google Pilot first/second-class medical standards to get a pretty good idea the ATC medical qualifications, pilot and ATC medical is pretty similar.
Being right out of high school will have no effect on joining. The vast majority of people who join the military are right out of high school. I don't think there's any age restrictions on ATC in the air force, but again you need to talk to a recruiter to be sure.