Likely contributing source for older people ("older" in this context can easily be as young as 35-40, but it gets worse the older you are): massive amounts of social stigma with the term "autistic".
It took me two years since an official ASD diagnosis in 2019 before I could apply the term to myself, and even now, 5 years later, it's still not emotionally neutral, the way that saying "oh, I've got brown hair" or "yeah, I get migraines too" would be.
The main reason? Suspected (still unclear how definitive) "autistic" diagnosis in the early 1980s that really screwed up my family of origin, and led to a lot of misguided and actively harmful treatment from them (both senses of the word: medical and interpersonal) for years.