@cheese_greater@lemmy.world @nostupidquestions@lemmy.ca

Perhaps your perception comes from the fact that we see/know few (if any) elder people who was diagnosed as someone within the spectrum. It's not because elder people couldn't be autistic, bc they can. In fact, not just they can be autistic, but there are lot of non-diagnosed elder ppl. Something to do with how autism (among other conditions) wasn't diagnosed until recently.

And even nowadays, it's still under-diagnosed: I myself, a 30yo male, may be autistic (actually, I'd be more of an AuDHD, if I'm not someone with Geschwind syndrome, given my auras, sudden spiritual experience, migraines, etc; neither conditions were diagnosed), but the only diagnosis I got so far were ADHD and, recently, Schizotypal PD, although the latter diagnosis felt more of a religious bigotry from a psychiatrist in a mostly-christian country upon hearing about my occultism.

There are other factors as well, as other reply pointed out: solar exposure. We NDs in general tend to be more introvert and homebound because the outside world may be hostile to us, so we prefer staying at home (we were #stayhome people before it became momentarily a widespread thing in 2020).

Why the under-diagnosing? Well, in the eyes of capitalism, it's not profitable to diagnose people with a condition that requires workplaces to be more friendly to our lack of social cue instincts, our different perception of spacetime, and our eccentric (non-linear) way of thinking.

Also, the lack of affordability and the inability to access proper (and non scripted (i.e. not restricted to trying to forcefully fit everything to a DSM-5 handbook)) healthcare. Even in countries where there is public healthcare (such as Brazil, where I was born), mental healthcare can be unaffordable, partly due to the cost of medication (which "Sistema Único de Saúde" (SUS, Brazilian public healthcare system) doesn't always have available for free), partly due to long waiting queue (I myself have been waiting for a psychiatrist appointment for more than a year; tried emergency/crisis healthcare places such as "Centro de Atenção Psicossocial" (CAPS, psychosocial care center, focused on dealing with mental health crises) upon self-harming and suicidal attempts, but they couldn't even begin to comprehend my multilayered and far-from-just-mundane complains; they replied to hour-long soliloquy, which involved me recounting my spiritual afflictions about the Demiurgic nature of existence and complaining about the Kafkaesque absurdity of this world, with "how's your pooping and eating?", and I'm not joke; at the time, I literally had a visible wound on my wrist, but all they could think about was my trips to the restroom and to the kitchen).

If an adult or older ND person can neither access nor afford mental health care, they can't be diagnosed, perpetuating a social situation of under-diagnosis that contributes to make it look like "only young people are autistic".