"I'm really distracted by the "decade since the Exodar crash" at the beginning, given Blizzard's tendency to squish the timeline in official sources, rather than draw it out. Buying world of warcraft account "
I play Atun on Wyrmrest, and I'm one of the players in Kharanei.
I /think/ that might have been taken from the guild timeline, rather than the official one (which is, as you noted, muddy.) During Cataclysm, some of the guild events caused us to split the guild timeline from Blizzard's timeline-- basically, we have Cataclysm lasting five years, but it was probably a year in game canon. It really doesn't come up much in current RP, though.
"I like to go with Velen being super special in his connection to the naaru, and other draenei are long lived due to the Light and their inherent magic, but "immortal" is not something I tend to like."
One of the NPCs in Bloodmyst
talks about one of the cities on Argus from memory and the Argent captive you talk to if you start a draenei death knight tells you to remember Argus in hopes of getting you to snap out of it, so a twenty thousand year old draenei doesn't seem to be uusual. My personal headcanon is that they're technically not immortal-- they do age very slowly-- but with a thirty or fifty or sixty thousand year lifespan they may as well be.
It's also assumed that most non-essential personnel were in stasis for a great deal of the trip-- one of the physically older members of the guild was born during the flight, WoW accounts for sale but was a cryo-pod technician, and so didn't go into stasis.