Early retirement incentive plans (ERIP) “seek to give incentives to older employees to retire before conventional retirement age. The purpose of these programs is to cut back on salaries and benefits to make way for younger workers.” While some ERIPs might constitute a prohibited act under the Age Discrimination in Employment Act (ADEA), the statute provides an affirmative defense for employers who can prove that the plan is voluntary and “consistent with the purposes” of the AcT.