“How often do people have sex?” Ideally, if people are to be happy in life, they have sex exactly as often as they desire. No more, no less. “People” is a variable. Sep 10, - suggests that it's this variable (age) which can predict how often we have sex. For example, people between 18 and 29 are having the most sex, with an "A scientist, though, would phrase the same question in an almost.