I'm not aging to improve flavor or texture, as said above, I'm just doing it to put it off or accumulate more. I keep them on their backs on the garage floor (moving closer or farther from the door to keep temp about 40) or in fridge in a meat tote.
I try to get to them within a week, but even 10 days is fine. I've never had a problem with spoilage or gut contamination with ducks or pheasants. Grouse (mountain and especially sage grouse) seem to get gut contaminated really easily, so I try to get to them asap. I think for sage grouse gutting them in the field is the way to go to ensure quality.