A regular pediatrician is a good starting point, but a developmental pediatrician may be what you need to get the best analysis. ADHD is not even looked at until medical issues like vision, hearing, and reaching milestones are considered and ruled out. It may be that he has no medical issues but has a speech delay and needs to be seen by a speech therapist. It may be that he is on the autism spectrum. He could have a combination of issues. It sounds like it's definitely time to get him checked out. And yes, some children do have a delay/disability in some areas plus above average intelligence. It's most challenging to handle both sets of needs, but it can be done.