What age is a puppy fully grown ?

Depends on the breed, some mature and develope slower than others. If you let us know what breed then someone is sure to be able to help more :-)

If you are asking about Cavaliers they tend to mature in height quite young around 9 months but their heads & bodies etc take upto 9 months more or longer depnding on the coat type & colour

Bitches heads seem to be quite immature when they are young more so than the dogs !