As of the effective date of this section, no person serving under a contract of unlimited tenure or similar arrangement providing for unlimited tenure at an institution of higher education shall be compelled to retire from such employment prior to attaining seventy years of age. In the event such person shall reach age seventy in the middle of a semester or fiscal year, such person shall not be compelled to retire prior to the end of the semester or fiscal year: Provided, That in no event shall such retirement be postponed beyond six months after the date on which such person attained the age of seventy: Provided, however, That nothing in this section shall be construed to preclude discharge of such person for cause.