Competition is not permitted until a dog is 12 to 18 months old, depending on the governing organization. This is because competition-level obstacles are too physically strenuous for a growing puppy . In training, young dogs are gradually introduced to the obstacles at very low levels. A dog must be under its handler's control since formal agility competition is done without a leash, and in some organizations without a collar. Practice sessions are conducted with the dog on leash until it is reliable.
Dogs jump according to their shoulder height.
Each organizaiton has its own scale. In Southern California there are several clubs and training schools that offer agility instruction. It is essential to start out with a competent instructor who will put your dog's safety and well being first. South Coast Agility Team is an Orange County practice club devoted exclusively to dog agility. We are not a professional trainer's group and do not offer classes.