I do believe that adults have a harder time grasping new languages. Their minds are cluttered with much more, and their brains are less plastic. Evolutionarily speaking it makes a lot of sense for children to be better at learning in general, as they have everything to learn.
I'm not certain Meppa is someone from the past that we knew, or maybe a lesser figure that only now plays prominent. His assumed amnesia certainly suggests he is a familiar, but who? My first guesses are almost certainly wrong - Moenghus, Cnaiur, Xinemus - all dead with little ambiguity, except for Cnaiur who was decked out in scars.
My money is on Meppa being either new or an old lesser character.