Is this me? Did I accidentially change my screen name?
Hallboy and I went through this just a few months ago–nearly identical situation: Hallboy graduated from high school, decent grades, not 100% sure what he wanted to do, but knew he wasn’t ready for college. He did end up enlisting in the Air Force (he’s now waiting to be called for BMT–that’s Basic Military Training for all you civilians).
To answer your question, yes, he can choose which trades he wants to learn, IF he scores well enough on the ASVAB testing and he’s qualified once he passes his physical. In Hallboy’s situation, there was a “slight colorblindness” (whatever that is) detected in Hallboy’s physical exam, and although this didn’t disqualify him from the military, it did disqualify him from some of the jobs he selected. However, he did qualify for several other jobs (and listed up to six jobs he’d like to do). Once he’s in and has experience under his belt, he can shift into another area if he decides to do that. (My son-in-law is also in the Air Force and did the same thing.) Another thing that may limit what he can do is if he doesn’t drive. (Hallboy doesn’t yet have his license.)
Hallboy has already decided that he will let the military put him through college–once he decides what he wants to do in college. Until then, he has the opportunity to get training for a career, get paid to do it, see a bit of the world, and get some decent benefits–all of which is more than many of the 18 year olds he knows can say.