There is no magic age in KY where a child gets to decide. A child has a voice in the matter, but not the actual choice. As to the weight of the child's voice--that is very case specific and something only the judge can decide. Ex: If child is wanting to go live with one parent b/c there are less rules to follow, a judge may not put too much weight on that. A judge must decide (generally speaking when discussing timesharing/parenting time) what is in the child's best interest and the child's wishes are only 1 factor to be considered. If this is an issue, you need to consult with an experienced family law attorney.
Responses are general in nature and do not create an attorney-client relationship. For specific advice it is advisable you retain legal counsel of your choosing.
It would depend on the law in the state where the child and parents are living. Some states have set guidelines for these situations, while others evaluate the maturity of the child on a case-by-case basis.