I had Micki in agility class when he was just over 7 months. My Aunt is an agility instructor and thought that Micki would be fine. I started going to classes with him, he was jumping 8 inches and I made sure not to do anything to strenuous and not a lot of tight turning etc...but something happened to him and he became lame. I am not sure if it is directly related to the agility training but he is now 3 years old, we immediately stopped all agility and have tried to find out what is wrong with him. We are still trying to figure it out, he has been in overnight for supervision, x rays taken of his whole body, etc but the vets can't find out whats wrong with him. He still has episodes where he will start going in circles and you can tell he is in a lot of pain, we take him to the vet whenever this occurs and he gives him a Cortisone shot. I think he is permanently injured from starting agility too young and he was perfectly healthy before classes began. I will never start a dog in agility that early again, I am actually going to wait until Jack is 1.5 years to make sure he has finished growing etc. For sport training I think it is much more beneficial to wait until the dog is older but basics can start right away.