Hi
              How old do dogs have to be to breed.The dog is a west hiland terriers.
              
                                    Thanks          

As with people Guest, jsut because they can does not mean they should :D  Just as a boy of 12 can father a child, and a girl get pregnant at 10 years old if her periods have started, the same is true of puppies.

A dog of this size should not be bred from until at least 18 months - two years if a bitch, and over 12 months if a dog.

Apart from physical and mental maturity they will be old enough to have been Hip Scored, and have any other breed specific health tests.

Also you won't know if they are good enough to breed from until at least that age.  Only around 10% of any breed will be of breeding quality. :)