The age at which horses stop growing varies depending on the breed and size of the horse. Most horses reach approximately 90% of their full adult height by the time they are 2 years old, and the remaining 10% of growth takes place over the next 2 or so years. By around 4 or 5 years old, most horse breeds reach their final height, but some tall, heavy breeds like draft horses may not reach their full height until they are around 8 years old. However, the bones determining height usually mature by four years old, and X-rays remain the most reliable method to confirm if a horse has fully stopped growing. Emotional maturity is also important for a horse, and most horses tend to reach emotional maturity somewhere around 5 and 7 years old.