At what age can a child decide which parent they would like to live with?

18.

Prior to 18, the court decides where the child lives.

This question has been asked and answered many times. So many in fact, that we have posted a sticky note at the top of this forum that answers the question. Did you bother to look at it?

In no state in the US can a child decide which parent to live with. Only a court can make that decision. Courts are charged with making that decision based on the best interests of the child.

Some states do have guidelines as to how much weight to put on the child's preference. But they are only guidelines.

If the child wants a change and the non custodial parent is agreeable then the NCP needs to file a request for modification of custody with the court that has jurisdiction. The court will listen to the arguments and make its decision.