The age difference between spouses has important implications in a variety of contexts - in patterns of marital unions, gender relations, marriage stability, and family configurations. This study investigates the main factors associated with age differences among heterosexual couples in Brazil, as well as their variations according to the sociodemographic characteristics of men and women by microregions. We used data from civil registry records from 1990 to 2019 and Demographic Censuses from 1991 to 2010. Based on the age differences between spouses, couples were classified as homogamous, hypergamous, and hypogamous. The chances of men and women being in a heterogamous relationship compared to a homogamous one were analyzed considering the following factors: age, migration status, education level, household situation, type of union, race/ethnicity, GDP, and urbanization rate of the microregions. Among the main results, there was a reduction in the proportion of couples where men are older, accompanied by an increase in couples where women are older than their spouses, regardless of marital status. There was also an increase in homogamy and hypogamy in marriages where both spouses are single. The postponement of marriages was identified as one of the factors contributing to changes in age difference patterns. Hypogamy was more common in consensual unions. When analyzing the variation of homogamous, hypergamous, and hypogamous couples among microregions, a positive association was observed between an increase in the average age at marriage of women and a high proportion of the female population over 25 years old with a college education, leading to a predominance of hypogamous couples. Other results associated with indicators of female autonomy and socioeconomic aspects indicate that the formation of hypogamous couples is not necessarily related to economically developed regions. The formation of homogamous couples was negatively associated with a high percentage of men and migrants in the population, while GDP per capita showed a positive correlation in this formation. Hypergamous couples showed a positive association with a predominance of men in the population and a high percentage of migrants. Regarding economic aspects, a negative relationship was observed with GDP per capita and urbanization rate. Considering the sociodemographic characteristics of spouses, the results indicate that men and women with a college education are less likely to be hypogamous and hypergamous compared to being homogamous. Migrant women are more likely to be involved with a younger man, while migrant men are more likely to be involved with both older and younger women compared to those of the same age.