On first read of your post I agree that nothing jumps out as "autism spectrum" to me. The early reading is not a red flag at all IMO (see my comments below). I would keep close watch on the social skills, though..Now that i'm reading your post for a second time i noticed it mentioned when i'd missed it the first time. And social is really the most important thing to look at..I say that because the social deficit is considered by most to be the dominant feature of spectrum disorders. Besides lack of interactive play, can you give more deails about his social skills. Can he wait his turn, show empathy, etc? is he like his peers for the most part? have good eye contact? Does he "herd" with them in preschool - like when they go do something he follows along, or is he very self-directed? If he is pretty much like his peers except he doesn't want to play with them, i'd think he is just a bit delayed there (no biggie). Or does he prefer adults? this might be because he could be very very gifted?

Also it is definitely too early to say "aspergers" which unlike the other spectrum disorders is usually not diagnosed until age 5. I have a son who is 7 and was diagnosed with PDD-NOS at 2.Many kids are diagnosed as PDD-NOS early on and look very similar but a few years later its clear who is AS, PDD-NOS, autism, etc... we are still struggling at this point if it is the correct diagnosis.

So i have pretty much read and re-read all the aspergers, autism, PDD-nos diagnosis criteria like a million times. Things that would signal aspergers would be pre-occupation with objects, extremely limited interests, resistance to changes in routine or things around them, atypical language development (though language may be very sophisticated), atypical social interest and development of social skills. What makes it different from autism and PDD-NOS is that the verbal development is usually very much ahead of everything else. I don't think "early reading" is mentioned in ANY of the diagnostic criteria for ASDs though it does seem to occur with a small percentage of ASD kids. Also the kids i know with ASD who were early readers were early "decoders" as opposed to truly being reading and comprehending. How is his comprehension?
irene