Although I wondered about it - didn't understand it - frankly, it never really mattered.
Somehow, Nancy managed to celebrate a dozen Christmases, a handful of Halloweens, and to cycle through the seasons so many times I lost track - and all without adding a single year to her age of 18.
And though I knew hers was the kind of world that existed only in storybooks, I still dreamed of growing up to be a famous girl detective - just like Nancy Drew.
There's something so satisfying about a series. Maybe it's the wonderful blending of the familiar (same core characters, same general themes, similar situations) with the inevitable surprises that a new story brings.
Or perhaps it's simply the fact that when it comes to books, there can never be too much of a good thing.
Not all series are created equal, of course.
But I'm pleased to say that 2005's offerings of new books for intermediate and teen readers did include two new series that could join Nancy Drew on my shelves.
If Heather Vogel Frederick's Spy Mice series is any indication, books that blend mystery and espionage are not going out of style. But they are definitely becoming more elaborate.
In Frederick's vividly imagined world of daring secret agent mice, scheming, villainous rats, and two fifth-grade outcasts, Washington D.C. isn't just the nation's political capital. It's also the headquarters for the Spy Mice Agency, where mice work to develop everything from spycam technology to aerosol-fueled jet packs - and keep the evil rats at bay. Think Stuart Little meets 007.
In the tradition of James Bond, the situations are semioutlandish, the villains are larger than life, and there are plenty of near-misses and suspenseful moments to keep readers turning the pages.
In the first book, "The Black Paw," fifth-graders Oz and D.B. must find a way to outwit the class bullies ("sharks"), or become shark bait themselves.
Meanwhile, secret agent Glory Goldenleaf is waging a battle against the king of the rats, Roquefort Dupont, in hopes of saving her father, mouse civilization - and her reputation.
The second book, "For Your Paws Only," offers up another duel against sharks and rats respectively, with kids and mice coming together in the end to foil yet another truly villainous scheme.
Although the series contains cartoon-style violence and involves an element of revenge, it's all par for the course in the classic contest between good and evil. There's plenty of humor, ingenuity, and affection thrown in to keep readers smiling and the good guys coming out on top.
For those who prefer historical fiction to fantasy, also of note is the new Portraits series from Scholastic.
In the tradition of the publisher's "Dear America" series, the books present a snapshot of a singular moment, era, or place in history (sometimes all three) as seen through the eyes of a particular character.
While the Dear America stories unfold through diary entries, the books in Scholastic's newest series are told by a third-person omniscient narrator, losing some of the immediacy that made Dear America so appealing.
But what 'Portraits' does offer is a superb blending of imagination with historical research. True to the series' title, each subsequent offering begins with a famous painting and builds a story around the girl or boy who features prominently in the piece of art.
For example, any museumgoer who's ever wondered about the identities of Degas's ballerinas can now go backstage with Sylvie Bertrand in Kathryn Lasky's "Dancing Through Fire."
Sylvie has dreams of becoming a prima ballerina, but when war breaks out in Paris, she's forced to question whether art is worth fighting for - and if it can help her endure the fight.
The second book, Anna Kirwan's "Of Flowers and Shadows," presents a slightly gentler vision of 19th-century life, although Aurelia Sandborn - the "girl" portion of painter Winslow Homer's "Girl and Laurel" - certainly has her own demons to confront, even living among the friendly folk of Townsend, Massachusetts.
Parents of young readers should be forewarned: This series is sometimes intense, and its authors don't mince words about history's darker side.
But its premise is both inventive and compelling, the historical details lush and engaging, and the authors succeed nicely at bringing together main character and artist in an uncontrived way.
For all these reasons and more, "Spy Mice" and "Portraits" will be joining the ranks of series worth starting - and continuing - at least when it comes to my shelves. I wouldn't go as far as, "Move over, Nancy Drew." But I might just say, "Meet your new friends."