I don't see it specifically mentioned so I will thrown this out there. I am a high school teacher and have talked with recruiters, etc. because they like to talk with my seniors. When a student is interested, the AF recruiter usually starts out by wanting to know the students GPA and what kind of classes the student is currently taking. Basically, slackers in the classroom need not apply (my words, not theirs). Then the ASVAB score comes into the discussion. I forget what the minimum is, but I believe its higher than the other branches (I could definitely be wrong). The Air Force is in a position to be very choosy right now and, in my experience, they definitely are.
Most of my students think of just "four" branches of the military, forgetting about the Coast Guard all together. I always tell them to consider all options.
Good luck no matter what he decides!