I don't know if this will be helpful or not but I want to post because I was there. When I was 19, I took the ASVAB for the Air Force, scored high, and was offered a choice of a couple of really cool jobs. I chickened out because of the no smoking policy in boot camp and I didn't think I could quit smoking.
I was a loser at the time, living at home and working as an auto mechanic but blowing all my money on stupid stuff. Many other things that I don't want to go into also contributed to me being a loser. Suffice it to say when you looked up loser in the dictionary you saw my picture.
My parents must have been pulling their hair out. I had all this potential and an offer of guaranteed training, discipline, and money and turned it down.
A couple of very dark years later I decided that I didn't want to be a mechanic forever and started college at age 21 and that was it, I just decided things were going to change. I turned it around completely. Put myself through school, secured gainful employment, got married and started a family, etc. Here's the kicker, I quit smoking on my own 5 years ago!!!
I'm not saying don't push him to get into the military; it seems like a great kick start for young kids. I'm just saying that if he decides not to go, hope is not lost.