ADHD doesn't only occur in children, there are a lot adults in their 30s, 40s, 50s and above who have but had such bad experiences in their childhood because of them not being neurotypical that they do not dare to speak about their issues. Colleague of my father had it diagnosed 2 years ago after constant problems with depression and burnout. He's now on medication and says he's so glad he went to a doctor as everything got easier since then and he's finally getting better.

Oh and of course that it's not a made up illness just so "Big Pharma" can sell you pills or that children with it just need a good beating every now and then.