Horses must be three years old to race in the Kentucky Derby. This age requirement is strictly enforced and applies to all Thoroughbreds competing in the race, whether male or female
. The official age of all racehorses in the Northern Hemisphere is standardized to January 1 of the year they were born, meaning all horses in a given Kentucky Derby are considered to be the same age regardless of their actual birth date
. This rule ensures a level playing field, although horses born earlier in the year may have a developmental advantage
. The three-year-old age limit is designed because by this age, horses have typically reached a stage of physical and mental maturity necessary to handle the demands of a 1ΒΌ mile race like the Kentucky Derby
. Horses usually begin racing as two-year-olds but only get one chance to compete in the Derby at three years old
. In summary, only three-year-old Thoroughbreds are eligible to race in the Kentucky Derby, making it a unique and age-specific event in horse racing
