Hmm, that's a hard one b/c he isn't giving you specific reasons why he doesn't want to skip. Having been through an IAS with dd12 when she skipped, I do know that the child not wanting to skip is an automatic disqualifier for further considering the skip.
I usually would say to not push it, but it does sounds like it may be in his best interests both socially and academically. He certainly sounds plenty able and high enough achieving and, with being on the older end for grade, he likely won't have major issues with being smaller or worse at sports which seem to be things people worry more about with boys. I can also say that, for my dd who was already the youngest in her grade, the skip worked very well both socially and academically.
Could you present it to him as a trial? Would they be willing to start sending him to 2nd after the holiday break since he is there for a good chunk of the day already? He might find that it isn't as big of a deal as he thinks and it might be less intimidating if it is presented as a temporary option you are trying to see what he thinks.
Do you think that it is possible that he is concerned that he will no longer be viewed as the smart kid if he is placed with older kids all day? My dd10, for instance, is in a 6th grade math class with other 5th graders (she's in 5th) and one 4th grader. The kids all think that the 4th grader is a genius. She also has a child in her GT reading class who, after starting K a bit later, skipped a grade & who is actually older than dd, but, again, the other kids are really impressed with how smart she must be to have skipped.
I don't know your son's personality at all so I don't know if losing his status as a "big fish" might be coming into play, but it's a thought. For my dd12, she isn't at the top of her math class after skipping, but she's as much as 2.5 yrs younger than some of the kids in her grade and she's still in the top 10% of her grade for math and still in the 99th for everything else. It hasn't put her in the position of being average.
Maybe reassuring him that it is uncommon for the school to recommend this and that the adults really feel that he will be successful in the next grade might help.
