How to treat the untreatable?

It sounds to me that if he's showing signs you need to understand the full scope of his disorder. It can range from just needing to be organized to serious learning disabilities. If I were you and I wanted to help I would be quiet and listen to his shortcomings. Understand what it is that he is missing. Go online, do some research on the disorder and then suggest midly that he incorporate some of these things into his life. Unfortunately he cannot retrain his mind at his age, but he can incorporate some much needed tools that will help him identify his challenges and finally overcome them. Good luck.