There is no age at which a child can decide whom to live with and impose that decision on the court. Such a major decision would be far too difficult for a child to make. Years ago it was permissible for a parent to ask the child to sign an affidavit of preference, which was nonbinding on the court, stating a preference for the parent he or she wanted to live with.
The minimum age for this was changed around a few times, and finally the legislature accepted the reality that such a heavy burden should not be placed on the child. Now, either party can file a motion asking the judge to speak with a child who is 12 or older, in which event the judge is required to meet with the child. If a motion for the judge to meet with a child younger than 12 is filed by either party, it is discretionary with the judge whether to do that or not.
As a general rule, judges do not like to meet with children because they recognize how traumatic this can be on a child, and such motions should not be filed except in extreme circumstances. When a judge does meet with a child, that meeting typically happens in the judge’s chambers, outside the presence of either parent or any of the lawyers.