The reason he’s older is just the opposite of why the quester is typically younger: his possibilities for growth are limited and time is running out. In other words, there is a time imperative, a sort of urgency as the sands run out. And then the situation in which he finds himself needs to be compelling.
This connects back to one of the first chapters in which the author explains why usually a protagonist who is on a journey is young---so they have the room and time to grow and develop as a person. Older people don't really have that much room and time, or they've already developed.
