 Zettl began his riding career in 1945, as a student of Herbert Aust.In 1950, at the age of 21, Zettl became the youngest person ever to be awarded the German Federation Gold Riding Medal, for success in upper level dressage and jumping for a single competitive season.In 1952, he was selected to compete for Germany's dressage team in the Helsinki Summer Olympics, but was ruled to be a professional rider and therefore ineligible.