The millennial cohort is roughly defined as those who were born in the 1980s to the early 2000s — although there is some debate about the boundaries. Millennials, due in part to their digital savvy, already are credited with significant changes in how we live, work and interact.

But what is particularly striking is how quickly the cohort has rewritten the rules for courtship, sex and marriage. In 2018, the median age of first marriage was approaching 30 (29.8 for men and 27.8 for women). That’s more than a five-year delay in marriage compared to 1980, when the median age was 24.7 for men and 22 for women.

A 2017 study in the Archives of Sexual Behavior found that many younger millennials in their early 20s aren’t having sex, and are more than twice as likely to be sexually inactive than the previous generation. Another study found that American couples aged 25 to 34 spend an average of six and a half years together before marrying, compared with an average of five years for all other age groups.