Penstemmon, it's strange but my grandson has no problem interacting with grownups. They all say what a fantastic boy he is, how grown up and polite. Teachers love him, always have done, but they cannot protect him all the time.
Hopefully, by the time he is older, those of his own age who are not so nice to him, and others, will be more grown up and polite themselves.
Once you leave school, you interact with people of a variety of ages and interests. It's only in the educational environment that you are thrust together with people your own age.
However, his chronological age is not necessarily the same as his ability and aptitude. That varied depending on the subject.
Even with trains, he will have a very interesting conversation with the driver of the Mallard, about the brakes, etc., because he has a train simulator and has learnt all the parts, then come home and watch Thomas. Then ask you what grin means , or what chuckle means.
Children with ASD are definitely individual.
I never understood when a teacher how I was expected to teach each child according to his/her ability and aptitude, in a class of 30+ for an hour at a time.