Any member in city-service who shall have attained the minimum age or period of service retirement elected by him or her upon such member's own written application to and filed with the board setting forth at what time, not less than thirty days subsequent to the execution and filing thereof, he or she desires to be retired, shall be retired as of the date specified in said application, provided that at the time so specified for his or her retirement, his or her term or tenure of office or employment shall not have terminated or have been forfeited, provided further that upon such member request in writing the member shall be granted a leave of absence from the date of filing said application until the date the retirement becomes effective.