Most Frequently Asked Question: What age does a child need to be to choose which parent to live with? – The short answer to this question is age 18, when he/she becomes an adult. Idaho Code does list the “wishes of the child” as one factor a Court should consider when determining the best interests of the child for custody purposes. However, it is only one of many factors. The Court tends to put greater weight on the wishes of a child the older the child is. Age 12 is when the Court’s usually will start putting greater weight on a child’s wishes and the weight increases each year thereafter.