Over in a nice discussion of the generation gap in SF on Tor.com, a commenter crunches numbers on the ages of Hugo winners and comes up with a pretty clear trend. Really fascinating, assuming you care about this sort of thing in the first place.
ETA: A handy graph, all color-coded and shit, via Tobias Buckell. Check out that eggplant-shaded sliver.
ETA2: Original thread now contains Nebula numbers too.
I don’t think you can read too much into those numbers without greater context. Author popularity plays a significant role in who wins which may skew the results to more established (older) authors. I’d like to see the ages of the nominees as well as the amount of time between an author’s first publication and awards before starting to draw conclusions.