As parents and physicians are so focused on development during childhood years, this may be why autism is said to be 'a condition of childhood'.
In undergraduate classes like Introduction to Psychology and Child Development, it is covered under childhood disorders. This is probably due to the fact that the condition (or state of being, if you prefer)manifests itself during early childhood. Oddly, as one of the most prevalent diagnoses, barely more than a paragraph is ever covered in "intro" courses. I spent more time learning about schizophrenia, PTSD, and mild mental retardation due to parental neglect than I did anything else.
Autism is certainly much more recognized than when I was growing up in the '80's and '90's, and I do believe it is in fact more prevalent. So at the current time, most of those with a formal diagnosis are children.
@ CrimsonWife, yes, back when I was growing up in the 60s, female ASD children were either misdiagnosed, labeled as disobedient or merely weird or as I was diagnosed with "atypical autism" The autism diagnosis was reserved for those who were entirely non-communicative or occasionally echolalic and who experienced severe and frequent meltdowns every day. So those of us who have been diagnosed even as children did not show up in the statistics from that time period.
Females routinely express the autism differently than males and for this reason were generally missed.
You make a good point.
@CBP I ask the question to whomever has an opinion. Even on this site (as in most others I have seen) the tendency when referring to autism is to refer to a child. We don't evaporate when we turn 21, and our needs and struggles may actually become worse. Many of us were abused as children, even at times unintentionally due to ignorance, and are cast out into a society that does not understand or care. We are typically unable to maintain employment, even if our skills are better than the competition simply because we do not fit in socially.