Welcome to YT! I found that all yorkies are different when it comes to hair growth... Two of mine (Jasmine and Butch) came to me with very short hair on their legs.... both of them have since had a "normal" growth of hair all over. Sometimes it just takes awhile.
As far as hyper-dog.... He may outgrow it... they seem to mellow out the older they get....
Best of luck!
