Does anyone know what age geese would outgrow this behavior?
It’s hard to say, henpecking is pretty common among birds, it can start in any bird, sometimes it resolves, sometimes it reappears only to disappear again, other times it never goes away.
Sometimes keeping them in a larger area can help to curb it, a lot of geese will tolerate other species as long as they don’t get into their personal space, other times if they’ve developed a hatred of certain birds or types for whatever reason they’ll never be safe around the goose.
For a few years I had the ducks living in the same enclosure with two of my ganders perfectly peacefully, but a few years ago they couldn’t be out in the yard together without the ducks obsessively bullying my female geese and the ganders trying to kill the ducks. My geese currently tolerate my ducks as long as the ducks keep six feet away.
Point is a multi species flock is a constantly evolving relationship.