He's claiming that childhood diagnosis is bunk. He's insisting that kids are unlikely to have ADHD.
I'm asserting that the behaviors for ADHD show up in children first and foremost.
I'm not saying that receiving clinical diagnosis as a child is the only way to have an adult diagnosis: In fact I'm not talking about diagnostics at all. It's that you _had_ ADHD as a kid, undiagnosed or otherwise, means you likely _have_ ADHD as an adult. I never once posited that someone with no diagnosis as a child is precluded from being diagnosed as an adult; however they should have had childhood symptoms based on the DSM as I understand it.
I'm arguing with someone who denies the existence of childhood ADHD in a naive "kids are just hyper don't drug them" argument.
It's easier for medical professionals to accept you have ADHD as an adult if you were diagnosed as a child, but that doesn't mean that all people with no childhood diagnosis cannot have ADHD.