DS is very capable of understanding the issues here. He's one of those kids who really thinks about things and understands stuff taht should be way above his head.

That said, he doesn't get full veto power over much. That isn't at all our parenting style. He's very much in favor of a skip to third next year. If skipping him mid-year against his will to save a few months is going to ruin the experience for him, I'd rather wait.