You have to be 18.
They have to be 18.
They have to be 18yo.
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
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.
You have to be 18 to decide where you are going to live.
18- 20 after 21 your on your own