when my ds was in 2nd he was accelerated 2 yrs in math and LA. He also enjoyed being with the older kids. It is hard to judge but I say let him go with the older kids.

I have to say I love Dudes response. "What does your DS say about this." I have been laughed at, had eyes rolled at me by the school for asking them "Did you ask my ds what he thinks", Ask him the same way you just asked me I would tell them.