Seems like a weird interpretation considering young people get all kind of mental conditions. I guess you're just not defining like depression, manic behavior or schizophrenia as cognitive impairment.... which comes of sounding weird to the layman perhaps?

I'm not surprised that a young person who can get schizophrenia can get Alzheimer's and have like this one reported cases shouldn't change perceptions much. That's how I interpret it at least. Plus you have young people born with learning disability and who get brain damage, it's not exactly an alien concept that young peoples minds get damaged very similar to adults.