Although I am not licensed in the State of Missouri, I will try to give you some guidance here. To my knowledge, there is no statute in any State which enumerates a specific age at which a child can chose which parent will have primary custody. While, yes, most Courts will take into consideration the preference of an older child, this is only one factor which will go into the Court's decision. The Court will typically look at the overall circumstances and base its decision upon what it believes is in the overall best interests of the child.
Sign up to receive a 5-part series of useful information and advice about child custody law.