what age can a child decide which parent to live with

I often hear this question.  The answer is that there is no age when a child can decide which parent to live with.  The court can change physical care (often called custody) only when there are substantial changes in factors bearing on the case which was not anticipated at the time of the court order.  Age is not a substantial change which was not anticipated at the time of the court order.  However, other changes may occur that combined with the age may allow the court to reconsider physical care.  If so, the court may listen to the choice of the child.