These are not books about adults taking advantage. They are about the complications of becoming one. “It’s up to you to decide what’s right and what’s wrong,” Katherine’s mother says in “Forever,” of losing one’s virginity. “I expect you to handle it with a sense of responsibility though … either way.”

Things changed. I became a teenager in the mid-1980s, as the AIDS crisis took hold, and I was a bit peeved to see this liberty fade away. The Reagan era had arrived, bearing its burden of endlessly multiplying — and sexually sanitized — series, or what my mother called “bubble-gum books.” There was Sweet Valley High (for which, as it turned out, I later wrote) with its size 6 Wakefield twins, and the lesser Sweet Dreams series, with titles like “Ten-Boy Summer” and “Lights, Camera, Love.” For history buffs, there was the Sunfire Series, where a love triangle might ignite alongside the Triangle Shirtwaist Fire. (Oh, how I loved the heroine of “Caroline,” growing up during the Gold Rush, who cross-dressed to pan alongside her brothers!) The Baby-Sitters Club and the Girls of Canby Hall presented the first Asian and the first black heroines in mainstream Y.A., which was revolutionary — but insufficient, sexually speaking. My mother retaliated by handing me “Tess of the d’Urbervilles.”

The ’80s did have accessible teenage sex, though: the camp goddess V. C. Andrews, whose books you had to sneak past your mother in the checkout line. They were not explicitly written for teenagers, but they sure featured them in starring roles. On each glossy black cover, a girl’s face peeked out from an oval cutout. Andrews’s teenage heroines would star in filth beyond your wildest imaginings: bare-butt spanking, torrid incest, rape-to-romance story lines. Who can forget the scene in which Cathy Dollanganger is brutally assaulted by her brother, Chris, an act that ignites a five-book, multigenerational incestuous love story? Who can forget “hill scum” Heaven, the protagonist of “Heaven,” and the predatory stepfather who becomes her true love? Or the heroine of “My Sweet Audrina,” whose parents have convinced her she’s her own younger sister to block out the memory of her rape? They made the later books in the “Twilight” series look like Nancy Drew.

Then, in the 1990s, Y.A. made its great leap into adulthood — to adult readers. It barely needs to be said what a titanic effect Harry Potter had on the culture, but one of its greatest achievements, or annoyances, depending on your point of view, was to make reading a family affair. J. K. Rowling’s series facilitated a golden age of magic and fantasy that endures. Series like Harry Potter and Philip Pullman’s His Dark Materials are brilliant, revelatory, hilarious, educational — great reducers of screen time. But they are largely sex-free zones that give new meaning to the term Planned Parenthood.

And pity those who look to this era’s love stories for succor. The most popular are studiously flesh-free. John Green’s “The Fault in Our Stars,” arguably the greatest romance of the past decade, gives its heroine a few lines to spill the details — and they are mostly to inform the reader she won’t. “The whole affair was the precise opposite of what I figured it would be: slow and patient and quiet and neither particularly painful nor particularly ecstatic.” Rainbow Rowell’s “Eleanor and Park” is lovely, but not the place where you will find words like these from “Forever”: “I need your written consent for the gonorrhea culture.”