Fewer things put me off a book more, even from a mere synopsis, than seeing a character with an anachronistic name. I’ve lost count of how many books I’ve seen, traditionally published as well as self-published, with painfully predated naming trends. It also annoys me when this happens to tv and movie characters.
I was guilty of this myself many years ago, but my excuse was youth and a pre-Internet age. All I had to go on were names I already knew and sources like that old baby names booklet and the even-more outdated set of 1965 encyclopedia. I naïvely assumed that the names I knew from my generation had been around for a long time, which I’m sure is what drives many older writers these days. I doubt everyone is deliberately predating naming trends!
Names like Aidan/Caden/Braden/Jaden, Madison for girls, Caitlin outside of Ireland and spelt in at least 144 documented alternate ways, formerly male-only names like Mackenzie, Jordan, Alexis, and Ryan on girls, and (my all-time least favorite) Nevaeh-it’s-Heaven-spelt-backwards-TEEHEEHEE!-isn’t-that-the-cutest-and-cleverest-thing-ever?! are all prime examples of predated naming trends. There’s no way I can believe in a teenage or college-aged boy named Caden or Braden (spell as you will), a contemporary teen’s mother named Madison, a 19th century boy named Ayden, or a 1950s girl named Dakota.
Is it that hard to look at the Social Security name lists for the year or decade your characters would’ve been born? You don’t have to become a full-fledged name nerd like I am, but you should at least have a general sense of naming trends from when your characters are supposed to live. If you don’t remember hearing names like McKayla (which literally means “son of Kayla” with that spelling) and Jaden when you were growing up, what makes you think they fit on characters from your generation?
There’s a big difference between using an uncommon or less-popular name and one that didn’t exist, or was only used on a certain sex. Names like Jennifer, Jessica, Amanda, Melissa, Nicole, Tiffany, Amber, and Crystal existed and were in use long before they cracked the Top 100. Some of those names also seem to have been used somewhat more frequently in Britain prior to their American explosion in popularity. But you can’t find names like Braelyn, Jordyn, or Amberly on the Top 1000 from a hundred years ago, because they didn’t exist. At least names like Jessica and Amanda existed, even if they weren’t massively popular.
However, you should be judicious with using recently-popular names in a historical, or even on older characters in a contemporary. I personally don’t have a problem with a few older/historical characters with names like Miranda, Stephanie, Nicole, or Jennifer. But if those are the only names you’re using, you have a problem. You need to balance them out with names that were actually common and popular then. In fact, using non-dated names for most of your characters works best. No one thinks of a Julia, Sarah, Elizabeth, Charles, Robert, or David as belonging to one particular generation.
Nicknames, like full names, also go through cycles of popularity. While the name Elizabeth never dates, there are about 20 nicknames for it. Depending on how old your Elizabeth is, or the era she lives in, she might have a different nickname than you’re used to. For example, a 1940s Elizabeth would probably go by Betty, a 1900s character might go by Bessie, a 17th century character might be Betsy, and a contemporary character would probably use the more familiar Beth or Liz. (Interesting tidbit: Buffy is actually a real nickname for Elizabeth!)
Not being a name nerd is no excuse for not having a basic sense of naming trends. If you can’t use a plausible name for your character, why should I believe in anything else in your fictional world? Sometimes a character’s name has to be changed. My Lyuba used to be Amy, and I’m sure most people are familiar with the story of how Scarlett O’Hara’s original name was Pansy.