Historical data on people under 30 who have had zero opposite sex sexual partners since turning 18

[Bernardo de La Paz]

15. (Certainly noteworthy graph) The OP was about "opposite sex", excluding same sex.

(Sorry Tom, not meaning to pick on you. As a programmer I'm almost reflexively detail oriented. And to be fair, even accounting for homosexual orientations, your contention probably still holds because of high proportion of heterosexuals.)

It certainly is a noteworthy graph. Makes me wonder too.

One explanation could be men on average have become less attractive, perhaps more long-bearded and rotund in some parts of the country. I read on DU the term "unfuckable" that some women give, occasioned by a photo in a thread of some rotund long-bearded guys occupying a state legislature with military-style rifles.

Or perhaps the percentage of homosexual men is considerably higher than previously estimated and young ones haven't figured out the codes to find mates.

Society has become more tolerant and accepting of homosexuality over many years, but the whole issue of sexual identity has become more tangled and yet more fluid (no pun intended) in recent years so there are more people being tolerant of their own sexuality and less self-policing.

Even so, media are a bit slow to catch up and the dominant depiction of sexual codes (flirting, come-ons, signalling) is still almost exclusively heterosexual.

Those two hypotheses are all I can think of at the moment.