(a) Any other provision of this article to the contrary notwithstanding, any person who first becomes an employee of an employer at age 60 or later may elect not to become a member of this retirement system. Such election shall be made in writing to the board within 30 days of first becoming an employee of an employer; otherwise, the person shall become a member of this retirement system. The election provided for in this subsection shall be irrevocable.

(b) Any active member of this retirement system on July 1, 1998, who was age 60 or older when he or she first became a member of this retirement system may elect to withdraw his or her membership and receive the total of his or her employee contributions with regular interest thereon. Such election shall be made in writing to the board not later than August 1, 1998; otherwise, the member shall remain a member of this retirement system. The election provided for in this subsection shall be irrevocable.