My down bags are a lot older than ten years, say 25, and still in (perfect?) condition, BUT I never ever stuff them ever - they just go into my 6500 inch pack and they are stored carefully and I have only washed one - my old blue kazoo, and it ruined the bag. I think maybe these bags are just carefully used.

The only reference I could find says that a down comforter will last 1-2 years if carefully handled.

As far as I know feathers are pretty much vacant from the archeological record and even feather items from Native Americans are pretty rare. I've seen Feathers on 100 plus year old arrows that are in pretty good shape though.
Jim