I agree that autism is a bit of a placeholder, much like the word “cancer” is. It likely describes a myriad of mental illnesses that are very similar yet completely different with little way to discern them for the time.
I think diagnosis tend to happen when a person’s issues start affecting their life negatively. With kids it could be schooling, attention issues or learning disabilities and since college is so important to obtaining a middle class life now, most parents are gonna do what they can to help their kids succeed there.
I do know plenty of people who were diagnosed very young, went through some therapies and were in mainstream schools by kindergarten as just a bit of a weird kid. But then the argument could be made that they might have grown out of their tendencies anyway (a good example is the flapping of arms, all toddlers do this and almost all outgrow it naturally by age 5-6)
I don’t think proper autism diagnosis come from neglectful parents, because parents who neglect their kids aren’t gonna notice that little Timmy can’t emote properly. Autism prevalence does go up in older parents though, It would be great to treat issues with personal nuance, and that likely happens in one on one therapies, but the reality is that:
1: in the US at least a diagnosis and label is necessary to get help from public schools and to be eligible for certain early therapies and schools that are helped out by the govt.
2: Humans love to label shit. It’s literally how our brain works and stopping that is really really hard. We don’t label to know what we are, we label to know what we aren’t, Its unlikely to stop, but you as an individual get to decide how much importance you attach to those labels.