For what it is worth:
At 3, my son was not interested in peers at all. He would notice babies and try to teach them math, and tell them they were cute. No interest in same aged kids at all.
He is almost 7, now, and interacts occasionally with peers, at school, etc. but in a very non-reciprocal way.
There is so much variance with spectrum kids, I wouldn't even know how to alter the norming of social milestones for the spectrum. I don't know if anyone has, although it would be nice to know, just for reference. I don't even know if spectrum kids follow the same social milestones, in the same order (I suspect they do, but I do not know) but in an atypical way, and obviously on their own schedule.