Mo. Rev. Stat. § 476.453
Any person having reached the age of sixty-five years and having served in this state an aggregate of twelve years, continuously or otherwise, as a judge or commissioner of any court mentioned in section 476.450, or having served in this state continuously for six years as a judge of any court mentioned in section 476.450 prior to the effective date of this section, shall, if he so elects, be made, constituted and appointed a special commissioner or referee for and during the remainder of his life, as provided and in the manner set forth in section 476.500, and when so appointed shall receive the same compensation as provided by law for special commissioners or referees, made, constituted or appointed under the provisions of section 476.450, and shall be subject to and comply with all the provisions of chapter 476 applicable to special commissioners or referees, the same as special commissioners or referees made, constituted or appointed under the provisions of section 476.450.
§ 476.453, RSMo