How old does a child have to be to choose who he wants to live with?

In Oklahoma a child can state a preference as to which parent the child wants to live with at age 12. There is a legal presumption that at age 12 a child has the mental ability and maturity to make the decision in the child's best interest. This is a presumption that can be overcome by the other parent if there is a reason that the child's decision is not in his/her best interest. An example would be the if parent the child wants to live has a drug/alcohol or anger problem or an unstable household. It is ultimately up to the judge to make the final decision taking into consideration the child's wishes.