Because horses mature so quickly, weights are necessary to let younger, weaker horses compete against their slightly older, stronger, and faster counterparts. By the time a horse reaches two years of age, it has reached about ninety five percent of its peak growth and strength, though it will not be fully mature until the end of its second year. That means horses closer to three years old are generally stronger and faster than horses that are six to twelve months younger. Because age plays such a large role in how well younger horses run, thoroughbred races use a mostly standardized Weight for Age scale. The scale was created in England during the 1860s and accounts for a horse’s exact age, gender, race distance, and the time of year when setting how much weight, or impost, to assign. The longer the race distance, the more of a natural handicap younger horses carry due to their less developed bodies.