The 'sexwave' was all of human history up to the Industrial Revolution... then another in the 70s with development of the birth control pill and no known significantly dangerous STDs. Interestingly, the USA was viewed as the vanguard of sexual progressivism in the 1970s and places like France were seen as provincial backwaters. There's a great book about Frances attempt to modernize their views to be more progressive called 'Good Sex Illustrated'. If you're interested in the ways in which sex education can be stilted to promote extremely conservative antiquated mindsets, it includes a multitude of examples. It is remarkably relevant because it's basically exactly what American educators and parents inflict on kids today.

They may be referencing the Summer of Love (1967) and the Free Love movement which was, if I had to put dates to it, 1966 to 1972.

During those times there were lots of people having lots of sex. Unwashed sex with a string scent of sandalwood and patchouli, but still lots of sex, drugs, and rock n roll.

Then you had the disco era, fueled by fruity drinks and cocaine, sideburns, and lots of finger guns. There was still a bunch of sex. Those people would become yuppies, while many of the Free Love people would have moved into the woods to eat tree bark and become one with Gaia.