I wonder if the adults, especially the women, are about to start appearing.
My guess is that there are a lot of people out there (and this may, but I can't be sure, apply to more women than men) who are being treated for quite serious depression and anxiety, and the roots of this may be adult autism / aspergers but nobody assesses them for that, they give them a pill, and if they are very lucky a few therapy sessions, and get them functioning just, and send them on their way. As long as you are scraping along and able to drag yourself into work and back that's ok, here take this pill and get back out there....sorry this is becoming a bit of a rant...
I grew up in the 1970s and 80s, at school I was slow developing reading, writing and maths, but not speech, and had mostly caught up by age 8, socially though I always struggled.
However, I was quiet, very polite, in-offensive, a bit nerdy and did not cause any trouble or disruption in class.
The social struggling was noticed and I was sent on some kind of odd 'self development' weeks course at 14 though no-one ever told me why I'd been selected for it, and it did little to nothing to address my social problems, and no-one assessed me for anything.
Now I may or may not have autism, I'm currently seeking assessment, but because I still struggle on and 'get by' enough then no-one has thought to assess me for it. Up until about 3 months ago I didn't know what high functioning autism was, and I thought only men could get Aspergers. And I consider myself quite well read and informed...
So I think this myth may have come about that people grow out of autism / adhd / add/ aspergers. This is just not true, I think people adapt, some very well, but the different ways of thinking and processing remain.
I also think that the fact that the fact that many societies now seem to expect:
1) You should have excellent social skills and emotional intelligence, but
2) There are no longer clear rigid writtten rules of social etiquette and politeness (not sure if these were a good thing or not) and
3) Nobody is teaching people what the current social rules are
puts people with poor social skills at a distinct disadvantage and makes life very much more stressful than previously.
I think the adults are out there, just not diagnosed yet, or only diagnosed with co-morbid conditions such as anxiety and depression brought on by the stresses and strains of living with autism in the modern world.
(edit for grammar / typo)