A:   Age at slaughter "typically" can be from 12 to 22 months of age for the high quality grade market. The reason for the range in age is that some calves are weaned and go directly to a feeding facility and finished for slaughter. Some calves are backgrounded, grown on grass pastures, then fed a high energy diet for a short period of time (100 to 120 days) then slaughtered. The two criteria that determine quality grade are marbling (intramuscular fat) and bone maturity. As a general rule, using typical feedlot finishing diets, as days on feed increase, fat in the carcass increases, and marbling increases. Just because fat in the carcass increases, doesn't insure that marbling to acheive a prime carcass. Maturity is determined by the hardness of the bone. In theory, an animal that is 24 months old animal that has enough marbling could grade "prime", "choice", or "standard", but not 'select". At 24 months of age, you are starting to push the maturity standard.