There is no magic age when children get to decide custody. The best interest of the child is the standard. The judge, not the child, makes the decision.
The law regarding a child's 'right'* to choose is a matter for each State and jurisdiction. The judge in most States, not the child, makes the decision based on the best interest of the child. Although not a standard by any means, many States have begun to give 'consideration' to a child's declaration of custodial preference when the child reaches the age of twelve or thirteen, sometimes fourteen. There are even cases when children of age 9 are allowed to testify.
The judge is normally given almost unlimited latitude in whether or not she or he listens to a child and how much weight to give to the child's wishes. In short, there is no specific "age" but the younger the child the less likely for a judge to give the stated preference much weight.
Good luck to you.
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In Texas, children have the absolute right to speak with the judge about their preference beginning at age 12. For children under 12, it's at the judge's option whether or not he or she thinks they will need to talk to the younger ones. Oftentime, though, judges want to talk with all of the kids at once, to get every child's perspective.
You father will need to file a Motion to Modify the current orders and to establish him as the primary parent (essentially, asking the court to switch the possession time between mom and dad). He should talk with a good family law attorney about whether or not his particular case would be one that could succeed based on the circumstances of his household, your mom's household, and the children's needs and best interests.
18. Until you are 18 the Court determines where you live. At 12 you can talk with the Judge, but the standard is what is in your best interest, not what you want. Your father would have to file a lawsuit to start the process. He could also file one to enforce his right to see you.