That all depends on how productive they are, living conditions, health history and how favourable they are to a producer's cow herd. Typically age of a cow is determined by the producer. If a cow is no longer productive for some reason or other, she is culled and sent to the slaughter plant. Occasionally a producer will let a cow, particularly one that is a "foundation" cow, live to old age. How old is old age depends on the cow: some will live until they are 15 to 20 years of age or more. Others may only live until they are 3 to 5 years because they had to be culled for health, temperament or unproductive reasons and sent to slaughter.