Lamb is the meat of sheep of either sex, usually younger than fourteen months old (younger than six months in Europe) with a dressed weight of about 65 pounds. Most lamb is brought to the market between the ages of five and seven months old, though baby lamb less than six weeks old is sometimes available. Spring lamb is from smaller lambs, usually under 50 pounds, that have been milk-fed.
Mutton comes from animals fourteen months to two years of age and is rarely available in America unless through a Middle Eastern market. Mutton is very strongly flavored, quite dark red in color, and fatty. Mutton can be used in any lamb recipe that calls for a long period of cooking, as time is required to tenderize this mature meat.