@quibling
I am hearing people say "I'm ADHD" when I'd rather they said "I have ADHD"
I totally get the argument against saying "he has autism" because it's not a disease, and its a fundamental part of the person. I get that its better to say 'he is autistic' instead.
But given ADHD starts for "Attention deficit hyperactivity disorder" it doesn't make sense to say "I am disorder" also, unlike autism, you can develop ADHD in later life, so its a different kind of thing.
AIBU to think this is wrong?
You are making a few mistakes here.
ADHD is understood as a form of neurodivergence with a close relationship to Autism. Many Autistic people prefer identity first language rather than person first e.g. Autistic person vs Person with Autism. This is because Autism can form such a key part of their personality. Similar language is preferred by many neurodivergent people with ADHD though there isn't really easily used language around it, like "Autistic". So you'll find lots of people say "I'm ADHD" or "I'm AuDHD" (Autistic with ADHD).
ADHD is poorly named, and sounds like a condition that neurotypical people develop like a disease. But it's not, it is a neurodivergence that is a fundamental part of the person. Like Autism it can't be cured. Medication doesn't change the fact that a person has ADHD, it just enhances the transmission of dopamine and improves function.
You cannot develop ADHD in later life. It can go unrecognised until later life having been masked or unrecognised previously. Some people might experience a worsening though life events -burn out, depression, menopause etc which brings the diagnosis to light, but it's still not new. Some people can develop cognitive deficits similar to ADHD as a result of brain injury, but again this is probably not the same thing as true ADHD which is ever present and associated with differences in brain structure and function from birth.
The bottom line though, is that people who have a condition are the ones who choose how they identify and describe that condition. You just need to respect that. They will have their reasoning as to whether they want to use identity first or person first language. Some people still prefer to describe themselves as having Asperger's despite the controversies around this. Working in mental health I always use the term the patient prefers