AC's policy is that minors must be accompanied, although on more than one occasion when I was under the age of majority I was questioned. If he looks close to legal age and acts the part he should be fine. This might be different in the states but that has been my experience so far. I second the point on dressing the part too, when i've been in suits and under legal drinking age I was asked for ID far less than when I travel in jeans and my university sweatshirt now as a young looking and barely of age traveller.