The governing body of any city of the first class, having a population of more than one hundred seventy-five thousand (175,000) inhabitants, is authorized and empowered by ordinance to establish a retirement system for all employees of such city and all employees of any board of such city, which employees are not already covered by the provisions of Kan. Stat. Ann. §§ 13-14a01 to 13-14a14, inclusive, as amended, providing for age and disability retirement, subject to the following limitations:

(a) To defray a portion of the cost of any such retirement plan, the governing body of any such city shall provide for a salary deduction of not to exceed five percent (5%) on all salaries up to the sum of four hundred dollars ($400) per month, for each employee;

(b) the monthly retirement allowance in any case shall not exceed one-half the average monthly pay such employee for the last five (5) years of his or her employment, nor in any case, the sum of two hundred dollars ($200) per month: Provided, This act shall not apply to any of the professional personnel not employed on a full-time basis.