At the expiration of two years after a retirement system pursuant to this chapter becomes operative, or on January 1, 1954, whichever is later, every safety member except an elective officer, the sheriff and undersheriff, who has attained age 60 shall be retired forthwith. On the said date a sheriff who is a safety member, is not an elective officer, and who has attained age 70 and an undersheriff who is a safety member and who has attained age 70 shall be retired forthwith.

This section shall not be operative in any county until such time as the board of supervisors shall, by resolution adopted by a majority

vote, make this section applicable in the county.