Mont. Code Ann. § 72-5-213

A minor 14 years of age or older may prevent an appointment of the minor's testamentary guardian from becoming effective or may cause a previously accepted appointment to terminate by filing with the court in which the will is probated a written objection to the appointment before it is accepted or within 30 days after notice of its acceptance. An objection may be withdrawn. An objection does not preclude appointment by the court in a proper proceeding of the testamentary nominee or any other suitable person.