hi does anybody know how old the drake is before he gets his sex feather?

I rather think they show when the birds get their
second lot of feathers... first feathers are generally
from 9 to 11 weeks second feathers about 6 weeks later
?
If you want to know to use as a means of sexing use the
voice instead by six weeks onwards ducks should be
able to quack if held by a wing tip or leg (but be
gentle) drakes don't quack even when fully grown.. they
make a noise but its not a Quack