The average life span of a domestic horse ranges between 20 and 30 years, though that depends heavily on the conditions in which the horse is raised and the breed of the horse. A horse does not reach full maturity until age 5.
The horse's general temperament can also affect its age. "Cold bloods," or horses with generally calm temperaments, can live much longer than 30 years. "Hot bloods," horses bred for speed and endurance, tend to have shorter life spans. "Warmbloods," a mix of the two, tend to fall squarely in average range. The verifiable record for oldest horse was held by an English horse named "Old Billy," who died in 1822 at the age of 62.