Young adult books have become the biggest thing in romance writing since--well, since erotica struck the shelves. Gunning for hits like Harry Potter and the Twilight series, anyone who isn't writing erotica is writing YA (and some are writing both, out of either sides of their keyboards).
The myth is in the reference, which implies that readers are approximately the same ages as the lead characters, maybe fourteen to twenty-four. But despite all the cute newspaper photos of kiddies dressed up as Harry and Ron and Hermione, Fiorella thinks the primary readers of the Harry Potter series were full-fledged adults. Same for Twilight, minus the costumes.
It's not hard for people to identify with characters younger than they are. After all, no matter how old we are, we still have all our earlier ages inside us.