Federal age discrimination law protects workers at or above a threshold age from discrimination in employment decisions.

Causation. Unlike some other federal statutes, the federal age statute requires but-for causation — the plaintiff must show the adverse action would not have occurred but for age. A mixed-motive instruction is unavailable. Many state statutes use a more permissive motivating-factor standard, which is a reason age claims are frequently brought under state law.

Comparators. Replacement by a substantially younger worker supports an inference, whether or not that worker is outside the protected class.

Code words. References to energy, fresh perspective, digital native, long-tenured, overqualified, and succession planning appear repeatedly in these cases. They are not automatically unlawful and they are always quoted.

Reductions in force generate the most age litigation, because selection criteria correlate with tenure and compensation. Cost-based selection that correlates with age is defensible in principle and difficult in practice.

Benefit plans. Older worker benefit protections restrict age-based distinctions in benefits, with limited cost-justification defenses.

Releases. Waivers of age claims require statutory formalities — extended consideration and revocation periods, written advice to consult counsel, and group termination disclosures. Defects void the age waiver specifically.