This paper shows the results of a field experiment in which over 6000 fictitious resumes with randomly assigned information about age (35-70 years) were sent to Swedish employers with vacancies in low- and medium-skilled occupations. We find that the callback rate begins to fall substantially for workers in their early 40s and becomes very low for workers close to the retirement age. The decline in the callback rate by age is steeper for women than for men. Employer stereotypes about the ability to learn new tasks, flexibility, and ambition seem to be an important explanation for age discrimination.