As the parent of an exception, I'll reinforce the idea that there are definitely exceptions -- our 4 year old is delayed -- and that it is definitely a thing. There is a fine line between the notion of "overdiagnosed" and "better understood". Autism is a great example of this. I've seen, elsewhere on these forums (though, grain of salt here, we're talking autism) that autism is everywhere now and is the new fad. Nah, we just know a lot more about it now. If I'd been diagnosed, as a kid, in today's world, I'd have been labeled as well. We didn't know nearly as much about the condition back in the 70s/80s, so I had to find my own way, and that's fine -- it works for most high-functioning people.
Playing the waiting game right now to see how close our daughter is to "normal" before she enters JK in Sept. She's come a really long way since we got SLT/OT for her, to the point where she can express herself a whole lot more than she could, but she's definitely not at a "normal" level for a four-year-old.