Cross-country variation in average retirement age is usually attributed to institutional differences that affect individuals' incentives to retire. We suggest a different approach. Since workers in different occupations naturally retire at different ages, the composition of occupations within an economy matters for its average retirement age. Using U.S. data we infer the average retirement age by occupation, which we then use to predict the retirement age of 38 countries according to the occupational composition of these countries. Our findings suggest that the differences in occupational composition explain up to 39.2% of the observed cross-country variation in retirement age.