I have two ducks (and a drake) that were hatched in April 2014, and two that were hatched in July/August 2014. In each pair, one girl is roughly three weeks older than the other. Got my first egg two weeks ago, and now have three of the four girls laying an egg a day. Not sure who the holdout is, but considering that at least one from each set is laying, they started at 9/10 months for the older pair and 6/7 months for the younger pair. From what I've read, it's not uncommon for the girls to wait until the early spring in the year following their hatch to begin laying.
Incidentally, my drake began mating the older girls in the late summer, and the younger girls in October when I added them to the flock, so mating isn't always an indicator that they are going to begin laying. I didn't notice any changes in appearance or behavior that indicated that my girls were about to start laying, and I think it was quite a surprise to them too. The first eggs always seem to be dropped wherever the girls happen to be standing at the time, but after a few days, they seem to get the idea and each began to build their own nest and bury the eggs for safe keeping.
