Hi Rocksea,
Parents often fret over the �small for his age issue�, but in my observation, that is less a concern than being far removed intellectually. My son was large at birth and is tall for his age (90th percentile). Even though he is young for his grade, you wouldn�t know it by looking at him. He is still ostracized by over 50% of his classmates. The reason is that he has many of the characteristic traits of children who qualify for the Davidson Institute YS program often have. He is not intellectually close to average. Even though he blends in physically, the other children have realized from day 3 that he is �different� and have treated him accordingly.
This is not to say he has no friends. He has a couple good friends and a few buddies. My advice is to early entrance or grade advance your son as early as possible to maximize the opportunity to bond with kids who are closer to his mental age. I think children are thwarted in their efforts to bully someone who is physically different by teachers and parents. I don�t believe that bullying based on the fact that another child is intellectually advanced is similarly discouraged.