Around what age do they get the curl tail feather?

[adorable]

For the call ducks. I know you can tell them apart for their voice. But i was wondering around what age do they start to get that curl tail feather to really tell them apart?

 

[Boggy Bottom Bantams]

6-8 months, not always reliable there though, vent sexing can be done at a day old, but easier with age as everything gets a little bigger and easier to see, bill color on some colors is a dead give away too, hens will have a loud quack quack quack quack , call, males are just a raspy muffled version.

What colors are you looking at sexing?