See if you can find an endurance ride that is going to hapen in your area or somewhere you can travel to. Go to the ride and talk to the people there. You'll find alot of poeple are willing talk and answer questions. Watch what goes on. F you can find someone that would be willing to teach and guide you in endurance that would be best. It's hard to get into endurance sucessfully without the help of someone who knows what they are doing. I've seen people push their horses to hard at a ride because they don't know what they're doing.
Also perhaps while you are waiting for your horse to be old enough you could approach some of the trainrs at a ride about riding one of their horses. Some trainers are always looking for riders for their horses. This way you can gain experience on an experienced enduance horse.
Endurance is a great, fun sport that is all about travelling imense distances with the horses health and welfare in mind. You do get the few odd poeple wh don't care about the horse. They just want to win. This is where the vet checks come in. They stop any horses from going any further if they aren't capable.