The old man is likely Zeus, if you read the trial votes you learn that Zeus was on the fence about what to vote for, so it's very plausible he came to regret his decision later. The whole being forced to do things goes with theme of recursion in which fate forces events to repeat, plus the twelve are likely loosing power and potentially "dying", Hermes might just be going senile at that point. P is absolutely not the P we know, it could have been his grandfather or maybe Poseidon. Zeus is Athena's father, so i'd read Hera's comment "pleasing the girl" as doting on his daughter.