Weight for Age (WFA) describes one of the conditions for a horse race. A horse carries a set weight in accordance with the Weight for Age scale. A trained official assigns the weight depending on the horse’s age, sex, distance, and the month of year. Such races are usually reserved for Group 1 races.
In Ireland, there are two prominent WFA races: the Irish Champion Stakes and the Irish St. Leger. In Britain, these meetings have WFA contests: Diamond Jubilee Stakes, Eclipse Stakes, July Cup, Sussex Stakes, King George VI and Queen Elizabeth Stakes, International Stakes, Nunthorpe Stakes, Sprint Cup, Queen Elizabeth II Stakes, and Champion Stakes.
Weight for Age is how officials equalize the physical maturity of horses, since thoroughbreds mature much faster than humans. Between the ages of two and three years old, horses will have reached their maximum height and weight. The weights serve to equalize the differences in maturity among the competing runners.
The extra weight a horse needs to carry will also eliminate the advantage or disadvantage of stamina, since mature runners tend to have more endurance. If no allowance was made, a mature older horse would always beat a younger one.