It really depends on the individual. Some go from no -verbal to making a living off YouTube/TikTok, some never really speak a lot.

Thankfully verbal communication isn't the only way to communicate. 6 is a bit early for that but, if your child ends up preferring to talk over chat or emails, try to roll with it, that could be the key to having meaningful conversations with him.

Personally, I can talk just fine but I'd rather not. Coming up with responses in real time and listening in real time is demanding for me, because I also have ADHD and my mind wanders around a lot. But if you give me a bit of time I'll probably write you a detailed, thought out answer like I'm doing right now. I can't handle small talk but surprisingly my numerous work meetings go well because I know all the answers, I'm an expert in my field and the goto for tough questions at work.

The main thing to keep in mind is that being non-verbal in no way means he's dumb. He can turn out to be very smart but kind of "locked in" unable to talk about it much but will write a solid PhD thesis like it's easy. It can be very weird how things play out, and too often people assume intelligence is a singular thing. Verbal intelligence and abstract intelligence and mathematical intelligence aren't the same, and autistic people tend to score low in some areas and very high in others, although not universal obviously.

Just focus on being a great dad and not force him into being neurotypical. We call it "masking", which is consciously doing all the little things people do unconsciously and it's exhausting. If he's being weird at home, it doesn't hurt anybody. Don't force answers or any task for that matter. We can be sensitive, and forcing things to happen at specific times is just stressful and can result in a shutdown or tantrum while you could have just given me an hour or two to mentally prepare and do the thing.

I see things like "my child refuses to go outside but we found him happily playing in the yard today, what's going on?" and the answer to that is, he did on his own will, that's the difference. He had the bandwidth and will to experience a bit of outside at this particular moment.