OP,
22 year AF vet here (still in, actually).
Thank you to everyone that went before me, but please realize the AF of the 80s, 90s and even 00s isn't the AF of today. We're downsizing left and right and it is pointless to get anything "in writing"...."needs of the AF" is always going to trump whatever the Airman wants.
So -- the recruiter can "promise" him mechanic or whatever job he thinks he wants but that may not happen in real life. Sometimes, he can do what is called a Delayed Enlistment, where the recruiter has him sign the paperwork now and then he reports to Basic in (hypothetically) January 2015 for a follow-on job in Vehicle Maintenance. If he reported to Basic this summer, for example, he'd get whatever job was open when he graduated, but by waiting, he gets what he wants, if all goes well. (Vehicle Maintenance isn't real big in the AF...bigger in the Army....we tend to contract out most of our car repairs)
He can certainly quit if he wants to, during Basic...there is no draft. But after that, he really can't without deliberately getting into trouble, to get kicked out to leave early. So he needs to know --- this is 4 years of his life, he can't quit and he might end up on backwoods North Dakota (no offense, Grand Forks AFB) and he can't leave. Or he might end up near Venice, Italy. Or Afghanistan. It won't be his choice. He won't get to choose when to go to work (could work midnight shift), when to eat (dining hall closes at X time) and where to live (in a dorm...he will NOT get to live in his own apartment as a new Airman).
The GI Bill does not pay out until 3 years have been served....so if he thinks "the AF will pay for my school", sure they will, but not right now. He won't be allowed to take college classes until he's been in a few years...at the beginning, they want you to learn your job, not take Biology and World History on your off time.
Can he pass the PT requirements? No joke, you have to be able to or you don't graduate Basic. Some American teens can't. (look them up on line, they go by age and gender)
Lastly, as a former Commander, I would not want your son in my unit. I say that plainly, because I had Airmen that were as you described your son....lazy, disrespectful, argumentative but always thinking they know better. Sure, Basic might help him overcome some of that but if he's an eye-roller, he may just smirk his way through and become a difficult Airman. All of his good qualities --- funny, big hearted, well spoken, well read -- are not going to make up for the fact that when I give him an order to go clean out the tool box and he rolls his eyes, or does a half-baked job, or mutters under his breath about how stupid this is, I simply don't need that. Because if he does that when I tell him to clean out the tool box, what will he do when I tell him to get down because a mortar is coming in? Or get in the convoy because we've got to go? Or fix a car for the umpteeth time....he thinks it's fine but the seasoned NCO thinks it needs one more check?
You have to take orders in the military...everyone does, except the Commander in Chief. Even 4 star Generals take orders and sometimes they don't like them but they do them. You know your son better than anyone...is he going to take the order or give attitude, etc? If he is, better for him not to enlist right now --- wait until he's ready. Because if you are a chronic problem Airman, you're going to get kicked out and possibly with a Less-than-Honorable Discharge, which will affect future employment.
Maybe instead of the military, how about AmeriCorps or something similar...where are aren't repercussions for not following orders? Something he can get out of, it it's not his thing? 17 is a hard age...you are expected to know what you want to do in life, but really, does anyone at that age? (I went to college, did ROTC so I had time to think about it). Today's 17 year olds are, I think, pretty convinced that they can do whatever they want and they'll figure out a way to make it happen, and unfortunately, in the military that's not true. I still encounter Airmen who are shocked that they have to work on a Saturday or do a "boring" job, or can't have their phone/Facebook while working in certain areas...shocked, because it doesn't fit with what they want to do right now, and they don't quite see why someone else has the "power" to tel them what they can and cannot do. But that's the military...and you go to jail if you disobey orders.
OP, your son has got to be a little stressed about what he wants to/is supposed to do next. Joining the Reserves might be a way to ease into the military....one weekend a month while in college, and he'd still get the GI Bill after 3 years. Then if he likes it, he can go active duty and if he doesn't, well thank you for your service, and best wishes. He could also do extra active duty time if he wanted, or just the one weekend a month thing....he'd have a lot more flexibility and choices.
Good luck to you both.