Lifespan and life stages

Depending on breed, management and environment, the modern domestic horse has a life expectancy of 25 to 30 years.[7] Uncommonly, a few animals live into their 40s and, occasionally, beyond.[8] The oldest verifiable record was “Old Billy”, a 19th-century horse that lived to the age of 62.[7] In modern times, Sugar Puff, who had been listed in Guinness World Records as the world’s oldest living pony, died in 2007 at age 56.[9]

Regardless of a horse or pony’s actual birth date, for most competition purposes a year is added to its age each January 1 of each year in the Northern Hemisphere[7][10] and each August 1 in the Southern Hemisphere.[11] The exception is in endurance riding, where the minimum age to compete is based on the animal’s actual calendar age.[12]

The following terminology is used to describe horses of various ages:

Foal
A horse of either sex less than one year old. A nursing foal is sometimes called a suckling, and a foal that has been weaned is called a weanling.[13] Most domesticated foals are weaned at five to seven months of age, although foals can be weaned at four months with no adverse physical effects.[14]
Yearling
A horse of either sex that is between one and two years old.[15]
Colt
A male horse under the age of four.[16] A common terminology error is to call any young horse a “colt”, when the term actually only refers to young male horses.[17]
Filly
A female horse under the age of four.[13]
Mare
A female horse four years old and older.[18]
Stallion
A non-castrated male horse four years old and older.[19] The term “horse” is sometimes used colloquially to refer specifically to a stallion.[20]
Gelding
A castrated male horse of any age.[13]
In horse racing, these definitions may differ: For example, in the British Isles, Thoroughbred horse racing defines colts and fillies as less than five years old.[21] However, Australian Thoroughbred racing defines colts and fillies as less than four years old.[22]