This would seem obvious, given that many religions (and denominations/groups/sects within those religions) forbid sex before marriage.
From the Journal of Social, Evolutionary, and Cultural Psychology (thanks for passing it along, Amy!):
Unbuckling in the Bible Belt: Conservative sexual norms lower age at marriage.
Abstract Sociosexual norms, as well as marital patterns, vary widely across human history and culture. Yet, humans share an evolved psychobiology of sexual motivation that reliably leads to procreation through incentivizing sexual activity. We predicted that in socially monogamous societies with conservative norms for sexual behavior, the interaction of sexual motivation and strong discouragement of non-marital sex would lead to relatively earlier marriages on average, as young adults seek a socially sanctioned way of expressing their sexuality. We examined this hypothesis with United States Census data from the year 2000. We found that cities in the “Bible Belt,” a region characterized by strong evangelical Christian sentiment, had significantly lower mean and median marital ages for both men and women, supporting our prediction. These relationships held when controlling for median household income, median family income, and even the operational sex ratio. We discuss our findings in terms of individuals minimizing discourse discrepancies and cognitive dissonance, to ultimately coincide with regional cultural norms.
Read the paper here.