What matters is not really whether a couple is married or not, but how long they’ve been in their relationship, whether they’re married or not. Couples of any age in the early phase of a love relationship tend to have a lot of sex—daily if not more frequently. But the frequency of sex declines as any relationship ages.
Interestingly, on average, married couples have more sex than unmarried couples, at any age. But the frequency of sex declines both with the age of the people in the marriage and the age of the marriage itself.
The frequency of sex for married couples reported in a 2006 survey went from about once every 2-3 days for couples between the ages of 18 and 29, to about twice a week for couples between 30 and 50, and less than once a week for older couples. But remember, these are averages. Some couples are happy with more frequent sex, some happy with less frequent sex. And that’s really the point: not how much sex you’re having, but whether you and your partner are happy with the sex you’re having.