Can a 12 year old Yorkshire Terrier go into heat?

Yes, a 12-year-old Yorkshire Terrier can go into heat, although it is less common as they age. Typically, female dogs go through heat cycles starting around six months of age, and while many may experience fewer cycles as they get older, it's still possible for an older dog to go into heat. If you're concerned about your dog's health or behavior, it's best to consult a veterinarian for guidance.