An aging population, coupled with low employment rates among Americans older than 62, poses severe challenges to the long-term sustainability of Social Security. Numerous reforms have been proposed to extend their working lives, including raising the retirement age. Such reforms may be unlikely to gain traction -- not because people are so eager to retire, but because age discrimination sharply limits job opportunities. After decades of debate, most labor economists today accept that discrimination has played a role in limiting job market opportunities for minorities and women. There's been a steady buildup of evidence that is hard to refute.