They have to be 18yo.
They have to be 18.
You have to be 18.
You have to be 18.
16
!* 18
They have to be 18.
Is that between a child's parents? if so it is ultimately up to the parents. But, most parents will let the child decide who they want to live with.
age 18 see links
In Missouri, a 16-year-old does not have the legal right to choose or decide who they want to live with. The court will consider the child's preference, but the final decision will be based on the best interests of the child as determined by the judge.
You used the word child. And legally they are a child and the parents decide where they are to live.
In Washington State, there is no specific age at which a child can decide which parent they want to live with. However, the court may take the child's preferences into consideration if they are deemed to be mature enough to express reasoned and intelligent opinions about their custodial arrangement. Generally, older teenagers, around the age of 14 or 15, are more likely to have their preferences considered by the court.
18- 20 after 21 your on your own