From LaBerge's "Exploring the World of Lucid Dreaming":
You may be wondering, then, how you could have a dream that seems to last for years or lifetimes. I believe this
effect is achieved in dreams by the same stage trick that causes the illusion of the passage of time in the movies
or theater. If, on screen, stage, or dream, we see someone turning out the light as the clock strikes midnight,
and
after a few moments of darkness, we see him turning off an alarm as the bright morning sun shines through the
window, we’ll accept (pretend, without being aware that we are pretending) that many hours have Passed even
though we “know” it was only a few seconds.[/b]
Dreams happen in the form of conceptual thought, thus, I believe it is possible to experience years worth of existence in a dream simply because you wouldn't actually physically experience it, only mentally.