My pekin started laying at around 20 weeks old, her first egg. Every duck can be different but usually in the 22-26 week range for laying. Make sure they get layer feed and access to extra calcium they can eat when they want.
For a previous comment, you can eat fertile eggs just collect them...
Stay away from canned veggies, way too much sodium for ducks. I had a pekin drake that had feathers on his leg and I just noticed one of my baby cayugas has a feathered leg too.