Would you have pulled your kid off?

I tend to side with the parent. There's a big maturity difference between 10 and 13. Sure, the kids basketball game would probably benefit if he played with older kids, but the rest of his education and development is a lot more important. Even if he's a phenom, he's still a long, long, LONG shot to make it in the NBA. There are plenty of examples of kids whose parents pushed them too fast and too far, and screwed up the rest of the kids life because of it.