dogs size

Question
Hello.  I just recently got a toy rat terrier.  I was told he was almost 5 months old.  He is already about 10 inches tall from floor to the top of his back.  That seems big for how young he is.  He weighs about 6-7 lbs.  I know they had a 3 year old mini rat terrier for sale also.  What is the size difference and also how long does it take for them to be full grown?  Thanks for your help.
~Katie

Answer
Katie -

I am not at all familiar with rat terriers, but found this page which describes the sizes.

http://www.centralpets.com/animals/mammals/dogs/dog3286.html

I would note, however, that not every size division is actually a different breed, so they could easily vary from one dog to another.

For instance I have seen Standard poodles who were only 35 lbs and minis who were 25.  My Jack Rusell weighs almost 30.

Most dogs reach their adult size (though they usually fill in some after this) by about 10 months.

-Beth