Jean Twenge, professor of psychology at San Diego State University and author of iGen: Why Today’s Super-Connected Kids Are Growing Up Less Rebellious, More Tolerant, Less Happy — and Completely Unprepared for Adulthood, said in an interview that growing sexlessness among America’s twentysomethings is primarily attributable to partnering up later in life.

“There are more people in their twenties who don’t have a live-in partner,” she said. “So under those circumstances I think less sex is going to happen.”

Americans in their 30s, 40s and beyond, meanwhile, are much more likely to be married than those in their 20s. These age groups are now considerably more likely to have sex in a given year than their younger peers.