To win the Equestrian you have to have the most points for dessage,jumping and eventing.
yes they do
the Olympics (eventing)
Equestrian debuted at the Olympics in 1900, missed 1904 and 1908, and came back in 1912 and has been an Olympic event ever since.
Galen Spencer was the oldest to receive equestrian medal.
Partial answer: The ages of the riders representing the United States in Beijing are given with their bios on the website 2008 Olympics Equestrian Cheat Sheet, http://www.theequinest.com/2008-olympics-equestrian-cheatsheet/
because it requires physical exertion