No person retired for service under Section 2.124.400 of this chapter or for disability under Section 4.124.410 of this chapter and entitled to receive a retirement allowance under the retirement system shall serve in any elective or appointive position in the city service, including membership on boards and commission, nor shall such person receive any payment for service rendered to the city after retirement; provided, that service as an election officer or juror shall not be affected by this section. Should any such person retired for disability engage in a gainful occupation prior to attaining the age of fifty-five (55) years, the retirement system manager shall reduce that part of his or her monthly retirement allowance which is provided by contributions of the city to an amount which, when added to the amount earned monthly by him or her in such occupation, shall not exceed the amount of the maximum compensation earnable by a person holding the position which he or she held at the time of his or her retirement or, if that position has been abolished the compensation earnable by the member holding it immediately prior to its abolition. (Prior code § 34.04.412)