I have ADHD, and I’m enrolled at a community college where I currently have a 3.9 GPA. I don’t take meds - I stopped taking them after I realized they were making me sick - and I don’t use accommodations. I did apply for them, just in case I needed them, but if your son doesn’t think he needs them, don’t try to force him to apply. The one thing that people with ADHD hate the most is feeling like they are being forced to do anything.
What your son needs really depends on his interests. If there’s a field of study that he’s truly passionate about, you will find yourself amazed by his ability to focus and get things turned in on time. I have a tendency to leave things to the last minute, but I do manage to get all my work in when I should. Maybe my experience is different than that of others who have been diagnosed with ADHD, but I have found that when my interest is piqued, nothing and no one can stop me for going after what I want. That being said, I did wait until I was 26 to go to college. I needed to see what else was out there first.