The original poster asked if anyone had any experience with the Air Force.
We loved our time as an Air Force family. I am sorry if you think it got off track. I just wanted to point out that there are always financial and emotional costs that come along with the service and, honestly, sometimes you aren't always aware of those costs until you are done with it all and can look back, which is the perspective that I am coming from as the spouse of a retired NCO. It is very clear that the original poster's relative is strongly dedicated to the idea of joining the military and as such, I would expect he has researched it. Wonderful! But the point is, it is a life of sacrifice, whether it is the small sacrifice of missing a birthday or anniversary or the big sacrifice of a soldier who comes home with PTSD or the ultimate sacrifice made by our fallen heroes and their Gold Star families. His mom's worries are real and not necessarily far fetched, though it's unlikely her son will come to harm.
To add one more thing, his mom may want to consider looking into the National Military Family Association, which is an awesome resource for military families. She can also, as the parent of a military member, get involved in a number of service organization. I'm not totally sure what the requirements for joining the American Legion Auxilary are, but that can be a great organization for spouses and moms of veterans. I think that moms and spouses of active duty would be welcome. Also check out Blue Star Families
http://www.bluestarfam.org/ and
http://www.whitehouse.gov/joiningforces/ for resources for family members, including parents.