Labrador retrievers reach their full height when they are between 12 and 18 months old, but they continue building muscle and filling out until they are 2 years old. How quickly Labs grow depends on the individual dog.
The American Kennel Club states that a standard fully grown adult male Lab stands 22 1/2 to 24 1/2 inches tall and weighs between 65 and 80 pounds. Female Labs grow to 21 1/2 to 23 1/2 inches tall and weigh between 55 and 70 pounds. Lab puppies need good nutrition for proper growth. Underfed puppies don't grow as well as those that are well fed, and a serious illness can stunt a puppy's growth.