Mo. Rev. Stat. § 70.650

Subject to the provisions of any applicable federal or state law the governing body of an employer may determine the mandatory separation age for its employees which shall not be less than the minimum service retirement age. Upon such separation from his last employer, a member who has five or more years of credited service in force shall receive an allowance provided for in section 70.655 and shall have the right to elect an option provided for in section 70.660.