Your son sounds like mine. My son has not been formally tested, though he is quite advanced, in maths in particular. He also has no 2e issues at all- he is a mature, responsible child, who prefers adult or older children's company, but has recently discovered the fun in age peers (like sports). Some children are different when they're babies, without it being "an issue".
On the other hand, if I had made a list of my son's milestones, it would have matched yours very closely, especially in the before-2 category. He now has an IEP for social/emotional development issues, and we are continuing to alertly monitor at home for the possibility of Asperger syndrome, although we haven't taken him to be tested for it.
The use of kindergarten is mostly social for a kid like this, but that can be a big deal. He may not make much progress on math, but he should learn to avoid dominating a group discussion while still participating in it, to stand in line when required, to shift tasks with everyone else even if he's "not done." I would probably not skip kindergarten - you would be better off skipping 1st or 2nd grade. But if he's not even 3 yet, you really don't need to know the answer to this yet, even if you want to. As annoying as it is, I think you just have to wait and see.
