snickers started biting/nipping at 12wks and has been steadily doing it since... but we are working on it
my vet yesterday (who has a terrier) said that terriers in general are a mouthy breed but v easily trained and not typically aggressive - i guess we just hafta establish ourselves as the "alpha dog" holding them on their back and getting them to calm down and let you do it puts them in a submissive position and grabbing the muzzle firmly and sat "no bite" then hold ur hand out and say "kisses" and if/when she kisses you reward her like crazy
i havent tried this myself so no guarentees but something to try
good luck