So I'm one of those players that loves backstory and associated characters and all that, and I've been playing an air genasi for a while with a djinn grandfather and human grandmother. My assumption has been that djinn were unaging, and that Granddad would far outlive Grandma and knew it. However, upon doublechecking with the canon sources I can find, this doesn't seem to be specifically stated, even for elementals!
In 3.5, djinn have the Outsider and Air subtypes. Are they unaging? Very long-lived? Has the current Caliph of all Djinn ruled for centuries, or longer? What about the other genies, and the elementals that populate the plane? I can only find one oblique clue: the chapter of The Inner Planes, written in the voice of an efreet, refers to humans as "you mortals."
I'm going with that for the moment... but does anyone have something canonical? Is a djinni or elemental ever explicitly stated to be immortial or very long-lived, or is such a character ever given an age category, or what?
Offhand, I can't recall a source that explicitly states it, I'm afraid. I've always DM'd games with genies being immortal, though - and now that I think about it, I've probably also assumed the same was true for games I've been a player in.
Classic stories of magic lamps with genies often have them trapped for looong periods of time. Would sort of be anticlimatic to rub such a lamp and get an ancient corpse deposited at your feet.