A sheep less than 1 year old, known for its tender meat. Baby lamb and spring lamb are both milk fed. Baby lamb is customarily slaughtered at between 6 and 8 weeks old. Spring lamb is usually 3 to 5 months old; regular lamb is slaughtered under a year of age. Lamb between 12 and 24 months is called yearling; when over 2 years, it's referred to as mutton and has a much stronger flavor and less tender flesh. There are five USDA grades for lamb based on proportion of fat to lean. Beginning with the best, they are Prime, Choice, Good, Utility and Cull. When purchasing lamb, let color be the guide. In general, the darker the color, the older the animal. Baby lamb will be pale pink, while regular lamb is pinkish-red. Lamb can be purchased ground and in steaks, chops and roasts. Lamb variety meats can also be purchased. Refrigerate ground and small lamb cuts loosely wrapped for up to 3 days. Roasts can be stored up to 5 days. Ground lamb can be freezer-wrapped and frozen up to 3 months, solid cuts up to 6 months.