The bylaws of a savings bank may prescribe a maximum age beyond which no person shall be eligible for election to the board of trustees and may prescribe a mandatory retirement age of seventy-five years or less for trustees subject to the following limitations:

(1) No person shall be eligible for initial election as a trustee after December 31, 1969, who is seventy years of age or more; and

(2) No person shall continue to serve as a trustee after December 31, 1973, who is seventy-five years of age or more and the office of any such trustee shall become vacant on the last day of the month in which the trustee reaches his or her seventy-fifth birthday or December 31, 1973, whichever is the latest.

If a savings bank does not adopt a bylaw prescribing a mandatory retirement age for trustees prior to January 1, 1970, or does not maintain thereafter a bylaw prescribing a mandatory retirement age, the office of a trustee of such savings bank shall become vacant on the last day of the month in which such trustee reaches his or her seventieth birthday or on December 31, 1969, whichever is the latest.