I wouldn't have thought it impossible to seemingly live a week or year or a life-time in a lucid dream. But to me the big brake on such a thing occuring is that evolutionary we are not designed to see the broad sweep of years or lifetimes ie we are designed to pretty much be in the here and now to hunt our food, avoid predators etc.

Sure we can conceive of the years passing but it still catches us off guard when we think "boy that year went quick" or "Shit, am I really turning 30!". We don't really see the year passing in front of us in the same way we don't see the grass growing. So I imagine it would be hard to drag such a conception into a dream. But maybe if you worked on it by writing out your life (real or imaginery) on paper so you can see the years flowing by like in a movie, and committ it to memory, it might help you take that into a lucid dream.