In most times and places, women on average, marry older men. We suggest a partial explanation. If the economic roles of males are more specialized than those of females, the desirability of a female as a mate may become evident at an earlier age than is the case for males. Males with good prospects will wait until their economic success is revealed before choosing a bride. Those with poor prospects try to marry young. In equilibrium, the most desirable young females choose successful older males. The less desirable young females have no better option than to marry available young males.