As far as I can tell from the responses so far I am the only one who actually has direct experience with this question. For the record, I enlisted at 17, did my three years, and (eventually) used the benefits to pay for a majority of my bachelor’s degree. Also for the record, neither the Army nor its representatives (recruiters) lied to me. They did, however, represent the best case scenario whenever possible. Does this surprise anyone? Read the fine print. Know the difference between a written promise and a verbal description. This is good general advice, not restricted to military enlistment.
On to the OP. Definitely tell him not to enlist only for the college money. He will spend several miserable years and perhaps sidetrack his life terribly. However, I disagree with the advice “go to the best college he can and use loans to pay for it.” Scholarships and grants are wonderful. Loans can cripple a person who struggles in or immediately after school. I have seen it happen. I would similarly caution against seeing ROTC as a panacea. An ROTC scholarship serves the right purpose, but if he has already graduated then it is probably too late to receive one. Without a scholarship, ROTC stipends are hardly enough to offset the costs of college to any significant degree.
Basically, it all boils down to the individual. Enlisting was the right choice for me for a number of reasons. The college money was simply a very nice bonus. If your student approaches it the same way, I would advise him to go for it. If he would enlist only because of the money, tell him to find another way. (In that regard, DO NOT rely on college financiall aid advisors to discover scholarship opportunities. The ones I have seen do not have the time or resources to do a thorough job and will always default to student loans for as much as the student can bear. Do your own legwork. If you want an education–work for it.)
This ran longer than I had anticipated, but it is obviously an important decision for the student in question. If you wish, you may pass on my email address to him. I do not claim my experiences were representative, but I will share them with him if he wishes.
The best lack all conviction
The worst are full of passionate intensity.