(a) observe the terms of a bona fide seniority system or any bona fide employee benefit plan such as a retirement, pension, or insurance plan, which is not a subterfuge to evade the purposes of this section, except that no such employee benefit plan shall excuse the failure to hire any person, and no such seniority system or employee benefit plan shall require or permit the involuntary retirement of any person because of age except as permitted by paragraph (b).
(b) require the compulsory retirement of any person who has attained the age of sixty-five and who, for the two year period immediately before retirement, is employed in a bona fide executive or high policymaking position, if such person entitled to an immediate nonforfeitable annual retirement benefit from a pension, profit-sharing, savings or deferred compensation plan, or any combination of such plans, of the employer, which equals, in the aggregate, at least forty-four thousand dollars.
(c) require the retirement of any employee who has attained seventy years of age and who is serving under a contract of unlimited tenure or similar arrangement providing for unlimited tenure at an independent institution of higher education, or to limit the employment in a faculty capacity of such an employee, or another person who has attained seventy years of age who was formerly employed under a contract of unlimited tenure or similar arrangement, to such terms and to such a period as would serve the present and future needs of the institution, as determined by it; provided, however, that in making such a determination, no institution shall use as a qualification for employment or reemployment, the fact that the individual is under any particular age.