I'm 24 and among my peer group, no one ever casually dated. You were either single or you were in a committed monogamous relationship. Maybe it was because we were all so poor in college, but no one dated. Almost everyone's relationships started when they decided to make-out one night and then the next morning they were in a couple that was exclusive. There was no playing the field, seeming more than one person or dating. Anyone I knew that was outside this mold considered themselves to be polyamorous.
We occasionally talk about how no one dates. The usual reasons we come up with are a lack of money and a culture obsessed with finding your one and only.