Darth Id said:
George's original conception was that the evil Empire was more or less timeless, and the whole Star Wars universe was based on the for-all-intents eternal struggle of the forces of good against the Empire.
I don't think there is anything in Star Wars, ESB or even ROTJ that necessarily contradicts this. Ben's yearning reference to a time "before the dark time, before the Empire" could be a reference to something extremely ancient and remote. There's no reason it wasn't 200 or even a thousand years before the events of SW, and Ben was the last of a long dwindlage of torch-bearers.
In that case, how old was Ben supposed to be?
Also, according to http://boards.theforce.net/threads/dark-empire-article-series-in-insider.50032523, Veitch initially wanted to write a comic about the Great Jedi Purge, and when Lucas rejected that, Veitch wrote Dark Empire instead.