I'd like to propose some definitions for your collective consideration.
1. Immortal: completely unable to die. Can be beheaded, burned at the stake, ground into the dust, etc., but will always have the ability to return.
2. Ageless: Not able to die through Natural Causes most notable of which: old age. However, can be killed by violence & physical destruction not caused by natural causes.
3. Deathless: see Ageless. Totally interchangable with Ageless. (the Heron Guards are referred to as "deathless" but we are certainly aware that they can be killed by violence). Also, Myrmidons are Deathless because although they suffer from natural decay, they cannot die from it. They must die from violence.
4. Mortal: (A) susceptible to death by any means. In this sense, the Ageless and Deathless are Mortal because they are suceptible to death, albeit in fewer ways. (B) anyone who is not Immortal nor Ageless.
5. Eternal life: a state in which one is no longer able to die from old age. This is the state of Agelessness/Deathlessness. The Heron Guards, Myrmidons, the Watcher, Myrdred, and most notable magic users have eternal life. This does not however imply Eternal Youth (see below), nor does it ever imply insusceptibility to death via violence. Therefore anyone with eternal life can die by means other than old age. So it isn't truly 'eternal' if you fall on a spike, but it's as close as we can hope to get to Eternity.
6. Eternal youth: a state in which a person retains his or her appearance, either for the entire endurance of life or in which the appearance of old age is extremely retarded throughout that endurance. NOTE: although the myrmidons were given eternal life, they were tricked by Balor and *not* given eternal youth, which is what they actually sought. People like the Heron Guard *do* have eternal youth in addition to eternal life. Hence their constant middle-aged appearance. Soulblighter had this, also. Because the Myrms didn't have eternal youth, they did not retain their looks and thus the body decayed. But the eternal life, which they *did* have, prevented the aging of the body to cause death.
Please consider these carefully and let me know what you think.
-Welly