Family social background factors influence age-heterogamous marriages across societies. This chapter examines how social background factors such as ethnicity, gender socioeconomic status, traditional marriage norms, and patriarchal family structure exert negative effects on age-heterogamy than age-homogamy in first time marriage in collectivistic societies. Using empirical data from Bangladesh as a collectivistic society, the results indicated that most of the couples were age-heterogamous than age-homogamous in first time marriages. The results of bivariate correlation and binary logistic regression analysis suggested that age-heterogamous marriages were significantly associated with social bacground factors. Of the predicting factors, ethnicity, gender SES, middle family income, arranged marriage, middle family size, patrilocal residence, and autocratic family authority were the greatest (1-3% times) risks factors for age-heterogamous marriages in Bangladesh. The findings have implications in future causal research and policy practice in Bangladesh.