In first marriages in the United States grooms are on average 1.7 years older than their brides, the life-cycle profile of this age gap is increasing both for the grooms and for the brides, and it is steeper for the grooms. To address these issues we construct a general equilibrium model economy in which people search for spouses, and they marry because they value bearing children, sharing their income with their spouses, and companionship. A distinguishing feature of our model economy is that the age distributions of singles are endogenous. We calibrate our model economy so that it replicates some of the aggregate features of the timing of first marriages in the United States. And we find that gender differences in fecundity are essential to account for the average age gap observed in first marriages. We also find that distributions of single people that are decreasing in age and some random matching are sufficient to account for the positive slopes of the life-cycle profiles of the age gaps at first marriage; and that gender differences in fecundity account for these profiles being steeper for the grooms.