Marriage and sex. Marriage, being with a partner a long time, and being older all decrease the frequency of sex.
Children can have a negative impact too.
Cohabiting, being in your late 20s, and being with a partner less than a year all seem to raise the frequency. So, let's put this equation to the test using data from the University of Chicago. In five years, that adds up to 520 acts of intercourse. Ten years later, they are far more likely to be having sex every couple weeks. But rates will continue to decline as both partners age and as they stay married for longer.