In response to the increasing fiscal burden imposed by public-pension systems, many countries have successfully encouraged older workers to delay retirement. These career extensions may significantly affect both the hiring and firing decisions of firms and the career progression of younger workers. To study these effects, we leverage reforms in the Netherlands in 2011/12 that gradually increased the eligibility age for public-pension benefits across birth cohorts. Using administrative linked employer-employee data, we first show that the reforms have significantly extended careers, doubling employment rates at ages that were directly affected. Next, we show that firms respond by delaying hiring, and hiring fewer workers overall. Co-workers also experience slower earnings growth over the period of career extensions, which is mainly attributable to a reduction in hours worked rather than lower hourly wages, but their separation rates from the firm are not affected.