Good lord. Could you imagine having to relive high school years ad infinitum?

I would think they continuously grow mentally because of having decades and centuries of experiences, which makes it even more ridiculous that they would keep going to high school. There are ordinary people who stop going to high school and never go back. Surely a vampire could figure out how to make that work.

Being immortal means they (and all other immortals) have to endure the heat death of the universe for effectively ever, so there’s that

I was referring to the original subject, tbf. Not in general. 🤷🏼‍♂️

Sounds like parasite apologia. I'm certain the animals you cited'd be fully against their slaughter, or those like them. This isn't a "nature does it" discussion here —especially since the creature in question is literally not of the natural world, ergo "supernatural". 🫤

Maybe you were unusual, I was attracted to people of my age as an adolescent.

Oh right I see.

Obviously the modern vampire has existed for just over 200 years and been told in many forms in that time.

It's been too long since I've read The Vampyre to be able to recall, and I've never read Varney or Carmilla to be able to comment on those, but the idea of vampires being emotionally stunted goes back at least as far as Dracula, where van Helsing monologues at length about the vampire's "child brain"—its simple-mindedness and almost instinctive/animalistic approach to going about its plans. And obviously you're already aware of how Rice's vampires are stuck at the age they were turned. Though as I write that, I wonder how that general trend in her books meshes with the portrayal of Claudia in Interview developing sexual feelings despite having been turned as a very young child. A retcon/something Rice developed more as the series went on, perhaps?

But anyway, my point is that the idea of vampires failing to mature is certainly not new as of Twilight or even the Vampire Chronicles. It goes back basically as far as the modern concept of the vampire. As for earlier vampiric folklore...van Helsing seems to talk about it as though he's discussing existing folkloric tradition in Dracula, but Stoker's idea of what that tradition was is very...idiosyncratic. It's hard to say how much that actually represents true folkloric beliefs, how much it represents Stoker's misunderstanding of said beliefs, and how much is the character of van Helsing. Regardless, personally I view the modern (post-Polidori) vampire as being so distinct from the folklore that there's not much value in comparing the two too closely when discussing vampires more generally.