You can best judge the age of a duck by pressing its beak with your finger. A young duck’s beak should be soft and flexible, while an older bird’s beak will be hard and firm. The legs should be smooth and the webbing of the feet soft and easily tom. A duck is a very fat bird, so you will need to use little additional fat when roasting. I usually cut all visible fat from openings before cooking, and pour off excess fat occasionally as it accumulates in the pan.
A good duck should have a plump breast, but it should not be over-fattened.