[Tina]

It depends on the size dog usuMedium-large dog breeds (Collies, Labrador Retrievers, Boxers) are fully grown by about 18 months and at their full weight by about 2 years of age. Giant dog breeds (Great Danes, Mastiffs) may take up to three years to reach their full weight, though they should be fully grown into their paws by about 18 months.

I personally changed over all of my puppies at age one but if I had known this information back then I would’ve waited until age 2.