The older kids wouldn't play with him either due to his age.
There is actually very little of this when a kid is single-subject-accelerated (SSA), for example placed in a higher grade for math... or has one or more years of full-grade acceleration (grade-skipping).
Please expand on this. I don't think I quite understand.
Sorry to be unclear. The reason other kids don't play with a child is rarely the difference in age, per se.
Kids interact with each other when they find things in common... including intellect.
Here is a roundup of posts on
acceleration, discussing pros and cons of kids being placed in a class or a grade level with older kids.