I also thought, that the old man should be Zeus, however, I just started replaying the game, and he's talking that he was a traveller in his younger age, and never settled down. So, assuming he's telling the truth, it's hardly Zeus: not the travelling god. :)
However crazy assumption: old man is Hermes. Let's just imagine, that's how he looks. And his 'Jean' look is just a disguise, or he transforms depending on his, let's say, sanity. Also, if I remember correctly, Hermes also started babbling in some unknown language in the infirmary, and also had shaking hands, and spilled coffee everywhere. So... maybe my assumption is not so crazy. :)
edit: Okay, I played through the whole prologue, and the more I read the less that idea seemed to be ridiculous...