NEW YORK (Reuters) - Promoting her new "adult" novel "The Casual Vacancy," Harry Potter creator J.K. Rowling finds it amusing that the most famous "adult" fiction of the moment is the erotic trilogy "50 Shades of Grey." But, she says, there's a big difference.

"The difference should be, people have sex in this book but no one really enjoys it," she said of her own book at a reading in New York on Tuesday night.

Rowling prefers to call her latest work a "novel for grown-ups," noting that she doesn't want readers confused into thinking she has moved from the magical world of Hogwarts to something more like E.L. James' wildly popular erotica books.

"The Casual Vacancy" is set in a small English town where class prejudices are played out and "grown-up" topics such as teenage sex, drug addiction and domestic abuse are addressed. It has hit the top of bestseller lists across the world despite mixed reviews since its release in September.

Asked at Tuesday's event the question many parents across the world are wondering - how young is too young for fans wanting to read her new novel? - Rowling said: "I personally would be comfortable with the right 14- or 15-year-old reading this book," but she discouraged those younger than that.

Rowling encouraged parents to be open to children dealing with fears through literature, and cautioned against sheltering children from certain types of books. It is "very, very wrong," she said, "to censor what a child reads from that point of view."

"If you are saying to someone, the thing that is in your imagination is wrong and dangerous and bad, I think you are saying to that child: 'You are wrong and dangerous and bad,'" she said. "Talk about it, feel it, and then dissipate it. That's the way to go."

Of course, that doesn't mean that young children should be reading "The Casual Vacancy," she added. "Well, that would be inappropriate."

She recalled a recent London reading of the new book when a 9-year-old boy was present, and she tried repeatedly to warn the audience that it was a "grown-up" book before reading a particular passage. "The f-word occurred roughly every two sentences," she said, raising laughs from the New York audience.

The seven books in the "Harry Potter" series have sold 450 million copies worldwide.

In its first six days, 375,000 copies of "The Casual Vacancy" were sold in the United States and Canada, according to a spokeswoman for publisher Little, Brown and Company.