By the time your dog is a year old, he's no longer a puppy. By that age, dogs have reached sexual maturity and they're finished growing. In most canines, the growth plates are closed by the age of 1. However, larger breeds take more time to mature, and their growth plates might not close until the age of 18 months or more.
Growth plates, located near the end of your puppy's leg bones, allow your pet's bones to grow. When he matures, these growth plates close and can no longer be seen on X-rays. Because the growth plate material is softer than bone, it's vulnerable to injury. That's why it's important not to stress young dogs with strenuous exercise. Once his growth plates close, he's ready for serious athletic activity.
Jane Meggitt has been a writer for more than 20 years. In addition to reporting for a major newspaper chain, she has been published in "Horse News," "Suburban Classic," "Hoof Beats," "Equine Journal" and other publications. She has a Bachelor of Arts in English from New York University and an Associate of Arts from the American Academy of Dramatics Arts, New York City.