Michael Barone writes for RealClearPolitics that the U.S. may be entering a new Victorian era, marked by reduced rates of teen sexuality, teen pregnancy, and hookup sex among college students. Perhaps, he says, we're seeing the end of the Age of Aquarius that began in the 1960s.
Trends do not continue forever. I suspect reduced teen sex has more to do with greatly increased time spent at a computer keyboard and may merely be the substitute of porn-enhanced virtual sex for often disappointing real in-person sex.
In Japan, where trends sometimes start, a near-majority of young people admit to little interest in real sex whatsoever. The Japanese birthrate is perhaps 50% of replacement level, by the way.