Small dogs usually reach their adult size a lot quicker than bigger dogs. I think the common wisdom is that small breeds are their adult weight and height between 9-12 months of age. Giant breeds can take 2-4 years.
Hi, I agree that they do mature much more quickly than the Giants, but they can still develop 'body' as such until they are 18 months or so...hope this helps a little? regards, Dawn (Owner of 2 Giant Newfies and lil ol Pepe the Yorkie!)