The custodian shall transfer in an appropriate manner the custodial property to the minor or to the minor's estate upon the earlier of:
(1) The minor's attainment of twenty-one years of age with respect to custodial property transferred under section 553A-4 or 553A-5;
(2) The minor's attainment of age eighteen with respect to custodial property transferred under section 553A-6 or 553A-7; or
(3) The minor's death.