Mo. Rev. Stat. § 287.830

Any administrative law judge or legal advisor who has served as such for less than twelve years and is otherwise qualified under sections 287.812 to 287.855 may elect to retire at age sixty-five, or thereafter, at a reduced retirement benefit in a sum equal to the proportion of the retirement benefit provided in section 287.820 that his period of service as an administrative law judge or legal advisor, or both, of the division bears to twelve years.