This video is great to show you how drakes sound:
It's how I learned "who" I had.
I have a rouen duck who didn't start laying eggs (that I know of) until she was approx. 10 months old. Watch out, ducks lay eggs wherever they want--unlike chickens who like a box. My duck was laying eggs in the woods, and in other not-so practical places. She could of been laying some for a while, and something could of been eating them. Keep them in a confined area until noon or so, by then you would know if you were going to eggs. So to my knowledge, I say- 10 months.