Thoroughbreds are brought to racing at two years of age, and are used on the tracks as long as they last. Colts and fillies of two, raced only in sprints until the fall of their first season of competition, frequently are referred to as juveniles. But the strain of racing at the speeds necessary to win today is so severe that horses, geldings and mares over six years are classed as aged. An animal of seven almost invariably has passed his peak and is beginning to go down hill. Five years or more of racing have taken their toll, and a player will be wise to make it a fixed rule never to bet on an aged horse. If such an animal seems the likely winner there is no sense in betting against him, either; the proper procedure is to pass the race. Of course aged horses win many races at all tracks in the country, but they are harder to train than younger animals, slower to come to hand, and hold an edge of physical condition for a shorter time. Also it never can be known just when one of these oldsters is going to break down.