I believe it was one terminal in Kill Your Television (M1) that introduced a key concept:
It was the soul (or essence) that was shared between all the heroes throughout history - not physical bodies. "Destiny" is apparently reborn again and again - with the likley possibility that the Marine is the final encarntion - having recieved God like powers at the end of time (Infinity's End screen).
Well, this wandered pretty far from the original topic. I mentioned the players age not as the primary point, but more of supporting evidence for how the rest of humanity would treat him given that his english dialect is at least 300 years out of date, regardless of his subjective age.
Unlike the chatty Halo Marine in his universe - our player is very silent. The only references to the player talking in Marathon cannon come from the Marathon 1 manual ... I believe. I also recal Yoss wrote a story whereby the player speaks to others on a desert world... does anyone know how much our [English] language would change in aporox. 300 years?
Its a concept not investigated in the Marathon series - nor any others that feature instant-space traval for that matter.
-Blayne