I've worked as a neuro tech for several years and have encountered a lot of autistic, ADHD, and epileptic children. The common age of the autistic patients for us was around 2 years old, but we dealt with them up to adult age.

I'm here to tell you that you are spouting harmful nonsense, and that there are definitely children that have a qualitative difference from their peers as described by 'autism'.

Overdiagnosis may be an issue, but that doesn't make it bullshit. Deal with the overdiagnosis on its own merits - but don't just start inventing stuff to simply make yourself feel better, because your misinformation can prevent others from getting appropriate assistance.