Well nobodies don't age right? For all we know the same could be true for whatever 'species' he is (Provided he is special)
Ah, well, there were no Nobodies before BbS, so he isn't from the past. And the Human Nobodies that we've see so far were all from the Organization, and they are all dead (or at least, no longer Nobodies).
And they had their abilities because they were Nobodies. That was the thing: "You loose your heart, but you gain the mastery over an element and you get weapons based on your previous self!"
It means that, with a heart, one does not have that weapon, nor does one have mastery over that element.
If the Mysterious Figure was Luxord, well, his Nobody is gone, and who's to say that his Heartless wasn't destroyed beforehand? In that case, Luxord's Somebody returns, however, he no longer has mastery over the time element. Nor can he manipulate cards the way he did in KH2.
Something I forgot to mention: I mean that he has to be a new character if he is indeed a Nobody.]