I wanted to know at what age a child can make their own choice about which parent they would like to spend more time with... legally.

A child can NEVER make the choice. This question has been asked and answered dozens of times.

In no US state can a minor child (under 18) make the decision as to which parent to live with. Only a judge can make that decision. Some areas have guidelines on how much weight to put on a child's preference by age, but the decision is still up to the judge based on the best interests of the child.

If the NCP wants to modify a custody order, they have to file with the court for a modification. The court will reviw the case and make a decision.

If we don't already have a sticky for this question then we need one. Legally, a child can not choose with whom or where to live that is up to their parents and if their parents can not stay together and agree then it is up to a judge but never a child.