There aren’t set age requirements for the Olympic Games; that is, the governing body of each individual sport sets its own rules regarding age. For example, the Fédération Internationale de Gymnastique (FIG) established the most current age requirements in 1997: gymnasts must be at least 16 years of age, or turning 16 within the calendar year, to compete in senior-level events. Diving minimum’s age is 14. While most Olympic sports do not have a stated age maximum, boxers age out at 35.
But before they had all those rules, a 10-year-old Greek boy named Dimitrios Loundras competed in the 1896 Olympics in Athens, winning a bronze medal in a team event and qualifying for all time as the youngest Olympian. As for the oldest Olympian, that honor goes to Oscar Swahn, a shooter from Sweden who competed in the 1920 Belgium Olympics at age 72 (he edges out dressage competitor Arthur von Pongracz of Austria, 72, by 232 days). He won a silver in the running deer double-shot team event. Swahn won six medals over the course of his career, which began at age 60.
In London, Hiroshi Hoketsu will be competing on the Japanese dressage team in an individual event at age 71. He will ride Whisper, a 15-year-old mare. Hoketsu will be the oldest Olympian at the 2012 Olympics, as he was in Beijing in 2008. The equestrian made his Olympic debut in 1964 in his native Tokyo. If Hoketsu has competitive aspirations beyond this Olympics, he will have to to qualify for Rio de Janeiro, Brazil's 2016 Olympic Games, in order to earn the distinction as the oldest Olympian of all time.