In all seriousness, those encyclopedias are hardly a source as most only take the films into accounts.
Its probably either the Sith Emperor (who I personally think is Palpatine as the Emperor is immortal age-wise)...
or Luke later on in the novels at his prime
or Darth Plagius (don't even go there with the whole killed in his sleep thing...he was sleeping...doesn't count)
or maybe even some of the original Rakata.