In horse racing

Depending on breed, management and environment, the modern domestic horse has a life expectancy of 25 to 30 years.[6] Uncommonly, a few animals live into their 40s and, occasionally, beyond.[7] The oldest verifiable record was "Old Billy", a 19th-century horse that lived to the age of 62.[6] In modern times, Sugar Puff, who had been listed in the Guinness Book of World Records as the world's oldest living pony, died in 2007 at age 56.[8]
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[6][9] and each August 1 in the Southern Hemisphere.[10] The exception is in endurance riding, where the minimum age to compete is based on the animal's actual calendar age.[11]
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.[12] 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.[13]
Yearling: a horse of either sex that is between one and two years old.[14]
Colt: a male horse under the age of four.[15] A common terminology error is to call any young horse a "colt", when the term actually only refers to young male horses.[16]
Filly: a female horse under the age of four.[12]
Mare: a female horse four years old and older.[17]
Stallion: a non-castrated male horse four years old and older.[18] The term "horse" is sometimes used colloquially to refer specifically to a stallion.[19]
Gelding: a castrated male horse of any age.[12]
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.[20] However, Australian Thoroughbred racing defines colts and fillies as less than four years old.