This question would apply only to GA. At what age can a child of a custodial parent decide to live with the non-custodial parent?

A child CANNOT decide. A minor child (under 18) cannot decide what parent to live with. That decision is ALWAYS made by a judge. Some states have guidelines about how much weight to put on the child's preference depending on how old they are. But the decision is up to a judge based on the best interests of the child. In GA a 14 yr old can express their wishes and it will be given full weight. If there is no fitness issues, the change will probably be granted.

Before a change can be granted, the NCP needs to file in local court for a modification of the custody order. A hearing will be scheduled and the judge will listen to arguments from the parents and may interview the child. Then the judge will hand down a decision.