You need to wait a while before putting the miles on that pup or risk permanent damage to her developing body. Assuming she’s in good overall health (your vet can help determine that), eight months of age is about the earliest you should start letting her run with you, and even then, you should figure on only a mile or two, at a relatively slow pace, at first. Keep in mind that the bones and joints of large or giant breed puppies mature more slowly than those of smaller dogs, so eight months is probably too early for them. Ask your veterinarian about the best time to get started if you have a large or giant breed puppy.
Even if running has to wait a bit, that doesn’t mean you shouldn’t be doing anything with your puppy now. Use the next few months to make sure your pet is well socialized. Introduce her to any situation that’s likely to pop up when you’re running; make sure she’s comfortable around people of all ages, bicycles, strollers, cars and noisy motorcycles. Free exercise on soft surfaces — such as play with another dog on grass — is also great for youngsters. Get your pup into a training class now so she’ll learn how to walk — and later run — on lead without dislocating your shoulder or pulling you off-stride.
Before starting any exercise program, talk to your veterinarian to get a more accurate assessment of your pet’s development and suitability as a running companion. When you get the go-ahead to start training together, take your time building up your pet’s mileage and speed. And keep your dog lean — even a little extra weight is harder on the joints. (And speaking of joints, make a note to talk to your veterinarian when your dog is mature about joint-care supplements. They really help!)
Honestly, I can’t tell you how happy I am to get a question like yours. Every day we see so many overweight or obese animals with a long list of associated health problems. Even for those pets who are not overweight, inactivity can be linked to behavior problems. It’s so great to see people who are making sure both they and their pets stay on-the-go and healthy!