My DD was intensely obsessed with math. It was insanity.

She also didn't bond with classmates until she started her current preschool at age 3.8 but she has always loved participating in group activities, especially circle time and lunch. She is now a bit of a queen bee and social butterfly at school. If she were still ignoring her classmates at age 4, I'd be rather worried.

Your DS is still very young but if you are concerned, I'd consider appropriate interventions.