Quote Originally Posted by AmonGwareth View Post
You are right, it isn't defined. Not really any reason to nail it down. It serves no official purpose. If, at some point, it becomes needed for in-game lore as part of a quest or story, then we will define it. For now, many hundreds. Which means you can RP it however you like.
D&D (3.0/3.5, don't know 4.0 sry) defines a lifespan of 2000 years to up to 4000 years, varying by race:
Dragon growth according to D&D stops about at age 1200 and at about a thousand to 3000 years (Time varies by dragon 'sub'race) they start to feel the effects of death by old age*. Most dragons however avoid that so-called twilight by departing (releasing their spirit and eating their entire hoard), becoming a guardian (by becoming a natural landmark) or becoming a dracolich (an undead dragon, only evil dragons would do that).

*) Each year after the defined Twilight Year the dragon must roll a DC20 constitution check. Failure = Permanent death; Success = Live further, lose 1 Constitution point permanently.
Source: Draconomicon D&D3.5

I'd rather assume that dragons for a fact are immortal and cannot die of old age because they are children of the realm of fire, an elemental plane. Being descendants of the fire element, it's imho doubtful that there's a time limit for the mind and body of dragons.
However, i'd rather assume that they grow old with time, being more pain sensitive when their growth has stopped and if their pain grows too much to bear, they'd rather release their spirits to leave the world of istaria forever. Gifted ones continue to grow until they become ancient but won't feel the pain of old ages.

There's one natural problem with immortality, though, but i'd rather not discuss it, because it would be against the forum rules.