B.W.
the age is about 12, BUT! You have to see the judge to change it all anyway and it is up to him if he wants to let a younger child make that choice. I have seen kids 8 years old pick a parent here in Idaho. I would go back to court and tell the judge the child wants to give him her opinion on it. It can be a private affair. I would also point out that the ex is trying to talk the child into moving back in so she doesn't lose the money.