(a) Except as provided by Subsections (b) and (c), an employer does not commit an unlawful employment practice by applying different standards of compensation or different terms, conditions, or privileges of employment under:
(1) a bona fide seniority system, merit system, or an employee benefit plan, such as a retirement, pension, or insurance plan, that is not a subterfuge to evade this chapter; or
(2) a system that measures earnings by quantity or quality of production.
(b) An employee benefit plan may not excuse a failure to hire on the basis of age. A seniority system or employee benefit plan may not require or permit involuntary retirement on the basis of age except as permitted by Section 21.103.
(c) This section does not apply to standards of compensation or terms, conditions, or privileges of employment that are discriminatory on the basis of race, color, disability, religion, sex, national origin, or age.