My DYDS 7 (just turned) skipped 1st this year and is now in 2nd. He is small and immature and ADHD. We were all worried including DS about the skip. The first week he kept saying that he felt weird and that he was not ready to talk to anyone in his new class. He also felt weird because somehow some of the kids knew he skipped and kept asking him why he was is second grade. But he has adjusted very well, made new friends, and his behavior has even improved a lot. So now after all the worry he is happy that he got to skip. He had a bad experience over the summer being the youngest at science camp, and we were all wondering whether it was a good decision, but I have seen him grow so much in the last 5 weeks. It is still a bit slow and too much work but he is participating in class again and trying very hard to keep up his good behavior.
We are still trying to figure out how to deal with the ADHD and improve social skills.
It is scariest right before the skip as you second guess everything, but for now it was the right choice.
The one thing that will make it easier for him is that your son knows that he wants to skip.