you will definitely find conflicting ideas on when to start dogs in agility..when I started my lab 12 years ago I didn't know anything and the trainer I was going to was basically just learning..I just wanted to wear out a 6 month old lab puppy and did a lot of things I now know better (putting a 6 month old puppy over a full size a frame
).. however I do start my puppies out from the time they come home...I generally have a play tunnel down a tippy board of some sort so they can use to the feel..I also start their foundation work along with their basic obedience..I start jump training without a bar and will progress to a bar on the ground and then a 4 or 8 inch bar as the dog progresses I start contact training with a flat 3 foot board and walking/running across a longer board on the ground..I start the bang game on the teeter..also I do a lot of ground work teaching front and rear crosses on the ground ..left and right..touch games..etc..so there is a lot you can do without stressing the dogs joints..and of course everthing is in very short increments..