Puppies can usually start walking short distances outside once they are around 12-16 weeks old and have received all their necessary vaccinations. It's important to gradually introduce them to walking on a leash and ensure that they are comfortable with the experience. Start with short walks and gradually increase the distance and duration as your puppy gets used to it. Additionally, be sure to supervise your puppy during walks and keep them on a leash at all times to ensure their safety.