Among first marriages in the United States, grooms are on average 1.7 years older than their brides. Traditionally, this fact is explained by sex differences in income. We use a general equilibrium, overlapping generations search model economy to show instead that sex differences in fecundity are essential to account for the age gap at first marriage, whereas sex differences in income play a secondary role. Our model economy also accounts for other facts on the timing of first marriages that the literature has overlooked.