Well he does sound cocky and that may make it difficult for you to get through to him.
One thing you said, that he mentioned, really stands out:
he just said not everybody is an alco like you. What could i say to that?
Perhaps that's a great conversation starter. All you have been through has probably taught you a lot, perhaps you understand alcoholism (if you think you need to understand more, there is lots of great information out there).
A reply might be - No, not everyone is an alcoholic, do you know what alcoholism is? I would then wait for an answer. He probably doesn't understand addiction at all at his age. I didn't, my Father was an alcoholic and frankly I never questioned it. You could tell him that he has a predisposition for alcoholism, that
anyone can become an alcoholic and once you do you are addicted for life (the pickle not being able to turn back in to a cucumber is a good analogy I think).
Many armed services are a hot bed for drinking, so perhaps his Mother's caution is not misplaced. Then again, it might just be the making of him. So that's an unknown.