It is not good to start repetitive jumping, contact hitting, or weaves until after growth plates have closed at maturity (or close) but flatwork, tunnels, and short jumps are totally fine in moderation. We don't jump in class or regularly, we just run through sequences. But the breeder said jumping below their elbows was fine up until a year, so we occasionally do a few jumps at 8", like this show and go. He's still got a table under his teeter and the poles open though, so no pressure there at all, and he only works on rubber matting usually.
Airn, nothing wrong with teaching solid foundations to pups, actually it is recommended. But there is a big difference in flatwork foundations and running sequences and piece work. Pups can learn impulse control, wicked recalls, shadow handling (heeling on both sides, at all speeds, walking, stopping, running etc) learning to run past obstacles and tunnel entrances without doing them is far more important at this age/stage than doing them. Plank work and developing a end contact criteria is also excellent. We also don't teach weaves to young puppies. Proofing recalls, stays and working during distractions, something as simple as tugging around other dogs or while other dogs are working. The hardest thing to do, is keeping your pup with you and focused on you in a distracting enviroment. We also want dogs/pups to look forward and not at us when doing agility, so a lot of work in put into teaching them to focus forward, it is called handler v.s task/obstacle focus. There is so much to train which can benefit a pup, regardless of whether you do agility for non competitive or with goals to compete.