* For small dog breeds: 7 years old is considered middle-aged.
* For medium and large dog breeds: 7 years old is often considered to be the start of their senior years.
Factors that affect aging in dogs:
* Breed: Smaller breeds generally live longer than larger breeds.
* Health: Dogs with health problems may age faster than healthy dogs.
* Lifestyle: A dog's diet, exercise, and environment all play a role in how they age.
It's always best to consult your veterinarian to determine the appropriate age for your dog's breed and health status.