The stigma of meeting somebody outside of your own "grade" has increased pretty severely over the decades. I would say that the age of consent issue has exacerbated this since people don't want to be perceived as a pedophile even though a couple of years difference is not really significant. So as the stigma increases you get people who refuse to look outside of their grade and end up finding nobody at all.
This article goes hand in hand with the "People are increasingly lonely" because 17 year olds are worried about dating 15 year olds.