Girl meets boy, girl falls in love, girl finds out boy is 500 years old.

Sound inappropriate? Icky? Creepy? Weird? Not for fans of romantasy novels, a subgenre that combines fantasy and romance, for whom an age gap of hundreds of years between a main character and a love interest is the norm.

With the arrival of megahits like “A Court of Thorns and Roses,” a series by Sarah J. Maas, romantasy has garnered a huge fan base. Many readers dissect characters like Feyre Archeron, the protagonist in “A Court of Thorns and Roses,” who is about 19 when she meets her 500-year-old “mate,” a mysterious faerie; they swap theories; and they rate sex scenes on a “spiciness” scale. Among them, there has been a recurring point of debate: Is it acceptable for a 19-year-old to date a 500-year-old?

Some say it is not only acceptable — it’s aspirational.

“I’ve made poor decisions with regular men,” said Asvini Ravindran, 31, a social media specialist who lives in Toronto and has a TikTok about books, including romantasy. “Why not make them with an immortal man with magical powers?”

Fans of the genre refer to such ancient love interests as “shadow daddies.”

Typically, the male creatures — vampires, faeries, gods, angels — possess dark and mysterious powers. They can be centuries old internally, but externally, they’re always young-presenting and, well, hot.

And these shadow daddies are desperate to be saved from their tortured pasts by the love of a spunky and yes, younger, female main character.

But what’s the appeal of a 500-year-old boyfriend, exactly?

Maybe real life. “It’s about the idea of someone who’d be mature and experienced enough to share the mental load with you,” said Elisabeth Wheatley, 29, a romance author and romantasy fan who lives in Austin, Texas.

She said that many women who read these books are in their late 20s to their 40s, with jobs and families to juggle, and sometimes lack support from a male partner to such an extent that it feels as if they’re “raising children and their partners as well.”

“I suspect the appeal of someone who’s 100 or 600 years older is someone who wouldn’t have to be taught how to apply for health insurance or fill out a car registration,” Wheatley said.

Then there’s the romance. Maddy Berry, 28, who hosts a podcast about romantasy called “The Smut Couch” with her friend Alexandros Ruppert, said that for her, the genre is a mental escape from the “u up?” text messages and Bumble profile pictures of men holding fish that constitute “dating in the human world.”

“So many men are swiping, swiping,” Berry said. Referring to the female protagonists, she added, “Seeing someone be so wanted, and being able to put yourself in those shoes, is magical.”

The shadow daddy figure is not a requisite of the genre. Plenty of romantasy books feature small or nonexistent age gaps, older protagonists and queer relationships. Some have a reverse age gap, like “The Invisible Life of Addie LaRue,” in which a 330-year-old female protagonist falls for a much younger man.

But enormous age gaps between younger women and older men show up often, including in popular books like the “From Blood and Ash” series by Jennifer L. Armentrout, the “Lightlark” series by Alex Aster, the “Hush, Hush” series by Becca Fitzpatrick and “The Familiar” by Leigh Bardugo.

Maas, the current rock star of the genre with more than 38 million copies of her books sold, makes liberal use of the shadow daddy trope.

In addition to Feyre, the late-teen heroine in the “A Court of Thorns and Roses” series, Bryce Quinlan, the protagonist in Maas’ “Crescent City” series, is in her mid-20s when she falls for Hunt Athalar, a brooding angel about 10 times her age.

For many readers, the acceptability of an age gap hinges on how deftly the author handles the power imbalance between the young female main character and her ancient love interest. Does she have magical powers? Does she have a life, interests, friends? Does he respect her boundaries?

“The last time an age gap bothered me was because the main character’s inexperience compared to the love interest’s was so emphasized,” Wheatley said. “I didn’t like her level of naivete.”

For example, readers who grew up with the worldly 104-year-old Edward Cullen dating lonely, inexperienced 17-year-old Bella Swan in Stephenie Meyer’s “Twilight” series have been reassessing the ethics of those books and movies — partially because Bella is a teenage virgin.

“He’s like a father figure to her,” said Ravindran, who recently rewatched the “Twilight” movies.

But Ravindran added that main characters in their 20s make sense to her.

“At 20, I would have happily run off into the sunset with the promise of romance and adventure,” Ravindran said. “If you asked me now, I’d be ordering a background check, I’d have to take vacation days from work and ask my husband if he’s cool with it.”