Yeah, that’s almost what the research articles I read suggested a few years back. Like, it’s allegedly difficult to diagnose an adult who has modified their behavior over the years. So most people would need to have at least some indication of having had ADHD when they were younger to confirm their diagnosis as adults.

That’s not to say that adults with ADHD don’t exist, but the rate does significantly decrease to about half.

(Please let me know if I’m wrong, it’s been a while since my days of genotyping.)