At what age is my dog considered a senior?

As we all know, dogs can vary from tiny little toy breeds to the giant Great Danes and Saint Bernard breeds. So really, the larger breeds tend to have a shorter life span in general. A giant breed dog may have a life span of eight to 10 years, so five years old is considered more senior. Whereas a smaller dog who has a lifespan of 14 to 16, it might be around the seven to the nine-year range that they become a senior. So it depends on what size and type of breed of dog you have.