ADD is not a single issue, but a collection of issues with varied symptoms and coping methods, and which he is likely experiencing to different degrees of severity. Thus, in my 20 years of experience coping with it, I've found the concept of ADHD to an unhelpful abstraction. Push past it and learn about all of the individual underlying issues and related concepts (attention and focus, memory (paying special attention…
One way to help him to do this work will be to get him out of his intellectual comfort zone. Encourage him to take on tough but fun projects (building big models, electronics kits, doing NAND to Tetris, etc) that will require foresight and planning. Make yourself available if he gets stuck, so that you can help explain that hard problems are only hard if you lack the mental framework required to parse and subdivide and organize them into simpler sub-tasks. If you can get him to sit back and think about how to solve hard problems, you'll be giving him a transferable skill which will be integral to working through life with ADHD and minimizing its impact--and you can do it without actually broaching the topic.