In the very beginning when I first started looking at other people's stuff, I used to think, "well...okay, maybe this person has this kind of influence" which makes them write in that style. Or maybe they watched too many forties style comedies or caught a Doris Day marathon. Watched the Partridge Family? Maybe their mom sounds like June Cleaver. I dunno. Lots of excuses. But I've finally come to the realization, people are strange.
They can look in a mirror and say, "Well, I'm of a certain age, but I still want to write about people in their twenties", using the idiom and attitudes of "my" twenties. Which would be okay, if they'd been a twentysomething in the eighties or nineties. Used the Urban dictionary? Talked to young people? Knew young people?
Like JR Ward. It's obvious she isn't in her twenties or anywhere close. I don't even think she's in her thirties, but she's got a grip on attitudes and dialog. In other words, her younger people don't ring false.
In the last couple months I've read fulls where the hero dwells (in a horrified way) on the heroine's "painted lips" and "tight sweater". The hero tells the heroine she can't cut the mustard--which might be a regional thing, but it originated with O. Henry, so to me it either means the author is a lit-major or grew up in a time period where it was the hot thing to say. The heroine can't be with the hero because she isn't pure (yes, in that way). The hero and heroine don't have cell phones, or know anyone who has cell phones, but they both have land lines. And use them.
I haven't seen one text, tattoo, piercing--junk food junkie, drive thru addict, energy drink-drinker, coffee groupie, water snob or game addict (even in extended family.) It's a squeaky clean, chaste, veggie-eating, pretty dress wearing world out there. Sure they might think "Hot Sex Now!" when they look at each other, but if one of them is chasing the other by looking up her address in the "residential phone directory", we have a problem.