You're also correct in that Asheron, even if he should be dead right this minute, certainly lived beyond his species' natural lifespan.
However, if he were using lifestones and/or vitae to keep himself alive, there would have been three profound and readily apparent effects;
Most people seem to have blithely assume that the Empyrean were immortal gods. Lifestones, however, can't [be] the solution to the mystery. Asheron possessed a unique longevity long before they appeared.
You're correct, the average Empyrean lifespan is approximately 1000 years.