Prefer to keep my old girls, and I consider old about 3yrs old, when they slow down laying dramatically. They become so special, each with their own uniqueness, it's hard to let them go, especially since they always seem to get eaten by a predator at a new person's house. However, it's impossible to keep all your favorites, so I have resolved to keeping just a few of the the most special. Right now, I have a white runner drake and runner/Cayuga bonded pair that have been together for 11 yrs now~and other than the drake's feet being a little more sensitive than his younger years, they are happy and healthy. The duck even laid a few giant beautiful Cayuga eggs this season.
Another option would to be to find a 4-H who wants ducks to show, and "gift" them some birds.
After having them for a year or years, I cannot stomach to eat them, there's no way, but this is my personal opinion. My favorite breed is Sandhill Preservation Center's Welsh Harlequin line...they are gorgeous, show well, lay well, and were calmer than Campbells.