169.563.  Retirement in certain systems at fifty-five or older with five years service, procedure, computation of benefits. — Any provision of this chapter to the contrary notwithstanding, any member of one of the Missouri retirement systems as provided by sections 169.270 to 169.400, or 169.600 to 169.710, who is fifty-five years of age or older, and whose creditable service is five years or more, may retire upon written application to the board of trustees of the retirement system in which he or she is a member and receive retirement benefits in an amount which is the actuarial equivalent of the normal retirement benefits the member would have commencing at the earliest date on which the member would be entitled to an unreduced benefit based on the member's creditable service at the date of the member's termination of employment.