Mo. Rev. Stat. § 56.824

Notwithstanding any other provision of law, any person who was a member of the system on August 28, 1989, who had served more than eight years as a prosecuting attorney or circuit attorney may elect to retire at age sixty-two at a reduced retirement benefit in a sum equal to the proportion of the retirement benefit provided in section 56.816 that the person's period of service bears to twelve years.