What is considered geriatric for a dog? The geriatric years for a dog are usually defined as 8 years of age or older. (For giant breeds it is 6 years of age or older.) The average life span of a dog has improved considerably in recent years.Today, it stands at 10 to 12 years.hat is considered geriatric for a dog? The geriatric years for a dog are usually defined as 8 years of age or older. (For giant breeds it is 6 years of age or older.) The average life span of a dog has improved considerably in recent years.