The following persons are eligible for the police retired list of a city and may retire as provided in this section:
(1) A person who is employed by any city as a police officer on July 1, 1975, is eligible for the police retired list when the person has completed 20 years or more in the aggregate as a probationary officer, a regular officer, or a special officer of the police department, in any capacity or rank.
(2) A person who is first employed by a city as a police officer after July 1, 1975, is eligible for the police retired list when the person has reached the age of 50 and has completed 20 years or more in the aggregate as a probationary officer, a regular officer, or a special officer of the police department, in any capacity or rank.