Many countries are incentivizing older workers to delay retirement, but relatively little is known about the spillover effects of these delays on firms’ labor demand and coworkers’ careers. We study a Dutch retirement reform that nearly tripled the employment rate at targeted ages, causing retirement delays of up to 13 months. Using population-level linked employer-employee data, we show that affected firms respond by delaying hiring of replacement workers and hiring fewer workers overall. Coworkers’ earnings also fall, reflecting the lower growth of their work hours, wages, and the overall incidence of promotions. Combined, the within-firm hiring and coworker spillovers are large and accumulate over time, offsetting more than half of the additional hours supplied by older workers. These spillovers exacerbate earnings disparities within firms, redistributing earnings from low to high earners, young to old workers, and women to men.