Mo. Rev. Stat. § 476.545: Early retirement, reduced benefit, how computed.

1. Any judge subject to sections 476.515 to 476.565 who is at least sixty-two years old and who has served less than twelve years and is otherwise qualified under sections 476.515 to 476.565 may retire at age sixty-two, or thereafter, at a reduced retirement compensation in a sum equal to the proportion of the retirement compensation provided in section 476.530 that his period of judicial service bears to twelve years.

2. Any judge subject to sections 476.515 to 476.565 who is at least sixty years old and who has served less than fifteen years and is otherwise qualified under sections 476.515 to 476.565 may retire at age sixty, or thereafter, at a reduced retirement compensation in a sum equal to the proportion of the retirement compensation provided in section 476.530 that his period of judicial service bears to fifteen years.