Much longer than you think
I’ve been looking at Dark Crystal: Age of Resistance stuff online.  One thing I see people speculating a lot about is whether any of the main characters are Jen or Kira’s parents. Â
I was confused, at first, why people didn’t realize that AoR is likely supposed to be many generations before the movie, when it occurred to me that the biggest clue isn’t actually mentioned in the movie itself.
I believe it’s mentioned in The World of the Dark Crystal, for one, though I’d have to reread it to make sure.  But especially, if you’ve read the Marvel Comics adaptation of the movie (also the novelization, I’ve been told, though I haven’t read it yet), you’ll know that when Jen remarks that Kira has wings and he doesn’t, she answers in more detail than her simple “Of course not, you’re a boy”.  She explains that female Gelfling used to be able to fly, but in the most recent generations, they can only glide and float.
The females in AoR can most definitely fly, so it must have been many trine ago*. (Though I’m somewhat annoyed that their wings seem noticeably smaller than Kira’s, while the other way around would have made more sense.)
Also, the AoR Gelflings’ ears are noticeably bigger and more mobile than Jen and Kira’s, so (in-universe, anyway, other than just a real-world stylistic design choice) they must have gotten smaller over time.
*I realize they may have changed their minds about the females’ later inability to fly, and you could chalk up Kira’s lack of actual flight to real-world technical issues, or even an in-universe lack of an older female to teach her how - but this is only my preferred take, after all, and I’d rather them not so blatantly contradict what was canon for so many years.
