How old do you have to be in 3 day eventing?

In three-day eventing, the minimum age requirement for horse and rider combinations can vary depending on the level of competition. For example, in the United States, riders must be at least 12 years old to compete at the Preliminary level and 18 years old for the Advanced level. Additionally, younger riders can participate in lower levels or in specific junior competitions. Always check the specific rules of the governing body for the event you're interested in, as regulations may differ internationally.