So, one thing that I've run into a few times among people who do fantasy worldbuiding (dnd players, fantasy writers, etc.), is very divided opinions on species with extremely long (or even immortal) lifespans. Some people hate them, and give everyone a similar lifespan, while others LOVE dishing out elongated lifespans. So what's the deal? Check out a very, very long ramble about long lifespans and worldbuilding under the cut.
TL;DR: To make them interesting, unique, and compelling enough to justify their extended lifespan in your world, your long-lived species should be strongly impacted by their long lifespan on a cultural and societal level, as well as strong potential for impacts on a personal level. Lean into that. Play around with it. If the culture of your long-lived species wouldn't change at all if they lived a human lifespan, you gotta change something.
I'm going to use elves from Dungeons & Dragons as my example here, but it applies to all kind of species across many many works and worlds. According to the Player's Handbook, D&D elves can easily live to be 750 years old. As in, that's their average life expectancy. Obviously that means that even longer lifespans are possible.
The PHB also says that elves "claim adulthood and an adult name at the age of 100". People have interpreted this many ways. I've seen takes that elves physically mature at the same rate as humans (what the PHB technically says), and "adulthood" is based on experience. (i.e., a certain level of life experience or worldliness needed to be taken seriously by other elves.) This works pretty well for D&D, because it provides a good excuse for your elven adventurers to be out exploring the world.
I've also seen a couple of takes in people's fantasy worlds or hypothetical situations where elves really do just age that slowly, including physically. (I once saw a post where someone talked about how weird it would be for a human to be babysat by a "teenage" elf, and have them be barely reaching adulthood by the time they die.)
Both of these takes have interesting implication, and most of what I'm going to talk about is applicable to both, although I personally favor the first option, so I might lean there sometimes.
But anyways. What's the "problem" with long-lived species? The most common take I see advocating against extended lifespans is either that it's boring (stagnant, what the hell do you do for 600+ years) or somehow unfair. Or perhaps most commonly, that they just don't know what to do with their long-lived species.
I would like to put forwards the argument that: If your long-lived species are boring, you need to play around with your worldbuilding.
There's just so many ways you can go!! Consider human progress: 750 years ago, it was the year 1275. The late 13th century. In the 13th century the Mongol empire was founded, Thomas Aquinas was alive, the Magna Carta was signed, and Cahokia's population potentially rivaled that of London. Oh, and the Ottoman Empire was founded.
Some inventions of the century: Wooden movable type printing was invented, as were earliest rockets and landmines for warfare, both in China.
And look at where we are today. Imagine watching that much progress happen within your lifespan. If you can remember the days before cellphones (or even just before smartphones), imagine that feeling multiplied by a thousand.
Now, I know that technological progress in fantasy settings is usually slowed, so that exact feeling might not apply. But think about it! How do your long-lived species feel about the progress made by others? Are they pioneers, innovating new techniques? Is there a single inventor (or a whole team) who's been working tirelessly to improve a single kind of technology (or spell/school of magic) for centuries? Are they slow to adapt, preferring to avoid using "newfangled, untested" technology? Are they jealous of what shorter-lived species can accomplish in their lives, or are they in awe of their ingenuity?
Obviously, cultures and species aren't a monolith, so there is almost certainly a range of these opinions across their society. Play around with it! Maybe there's a band of staunch traditionalists (or even extreme nationalists) who oppose the use of any tech or magic not created by elves (or whatever long-lived species you're talking about). Maybe there's an elven philanthropist who has spent centuries expanding their network of charities and safety nets, knowing that they can help so many more people in a lifetime.
Consider how your elven/long-lived species integrates with other societies. Are they mostly isolated, living in elven-majority nations? Or are they spread out across the world, living side-by-side with shorter-lived species. How do they feel about their shorter-lived neighbors? (both on a larger, international scale and a small, building scale) How do their neighbors feel about them? Does the long-lived species find short lifespans beautiful? Tragic? Disdainful?
Again, you're going to run into a range here. Maybe there's an oddball elf who moved into a majority human village and has been like, their weird community uncle for the past 300 years. He knows everyone in the village by name, and mourns every death, even though he's seen so many. Or maybe there's an elf who was scarred early on by the loss of their shorter-lived friends, and now they stay isolated, refusing to interact with anyone who doesn't share their long lifespan.
Maybe there's a mad elven scientist who desperately wants to find a way to share their long lifespan with their loved ones. Do their loved ones actually want it?
And that's just a societal level. We haven't even gotten into the political or personal level. Imagine the power of a grudge or a wound that has been festering for centuries. Hating another nation even though the regime that wronged you was overthrown centuries ago. Or demanding someone honor a treaty that was signed before their great-grandparents were born.
Imagine a character who can't grow or change or let go of their hurt. Instead it grows, setting down roots. (AMC's Interview With The Vampire is an excellent example of this. You never change, never get better. The cycle of abuse continues for eternity, a dance following the same steps over and over and over again.)
So me and my party and running Tomb of Anniliation right? And we are sitting in Omu just kinda having a long rest (one of our party memebers had to leave early). So Jescena (our sorcerer) starts talking to our eladrin NPC, just kinda talking about life and such, when she remembers she has a bottle of teich in her bag
(Please note that we straight up told this NPC that our party members were all raging alcoholics)
Biero (the eladrin) refuses the tiech, claiming it will make his personalities funky, and we accept that and give him water instead so he can still drink with us. We love this dude by the way.
However the topic of ages comes up, considering most of my party consists of either angels or elves.
Andromeda (our Elven Ranger) started saying she was about 230ish, to which Jescena replied that she was closer to 400. Interested, Biero responds that he's nearly 950 (super old dude, but seriously this guy is an eladrin bladesinger. What a fuckingman)
Please note that I am playing a half-elf bard, who this whole time is just kinda strumming, reaching for her shot and all that shit.
But when Biero said his age, my character Jaqueline looked him dead in the eye, said "I'm 18 motherfucker" and downed a shot.
My DM was so surprised that he just accepted it at first, before whipping back and giving a really started reaction. I found it quite hilarious.
