Hello and thank you for your question.
There is no set age at which the courts simply defer to the child, however, as children get older the courts are more inclined to give weight to their preferences, particularly if their reasons for preferring one parent over the other are reasonable, and it would be fair to say the courts will be reluctant to go against a child's preferences from around age 13/14 unless there are compelling reasons against the child's preferences.
Younger children may also get their way if their reasons are compelling but the court will be more suspicious that they are being influenced by a parent seeking custody or because they have an unrealistic notion of the issues. For example a younger child who prefer's Mum because she lets the child stay up late, may have their preference disregarded, however, the child who want's to stay with Mum because Dad leaves the child alone at night may have their preference given great weight.
One thing to watch out for, however, is that the court will take a very dim view if the court forms the view that a parent is trying to influence or coach a child in a way that undermines their relationship with the other parent.
In your case, I think you need to talk to your child and try to understand what the problem is, and if it is something that ought to be fixable, to take it up with the other parent to let them know what it is that is upsetting the child.
I trust the above assists.
Good luck and please rate my answer.
children are not generally allowed to give direct evidence to the court, rather a court appointed psychologist/counselor interviews children and then reports to the court about the attitude and of (this is so as to avoid the trauma of a child having to testify against a parent in open court).
A court will take the report on the child into account, but whether it regards ***** ***** as decisive will depend on what the report says. Older children tend to have clearer and more rational reasons why they prefer one parent after the other.