Will Falconer, DVM Moderator
Great question, Mary. Dr. WhiteCoat has been shifting the definition downwards over the years, as he creates more and more chronic disease, largely from over vaccination. Younger animals are now getting what used to be old animal diseases and infirmity, so 7 or 8 is likely "senior" in a lot of conventional medical practices now.
Truth be known, if your 7 year old has already had several rounds of shots, he's done. For life. Reread those quotes from the vet immunologists to understand why that's been true for decades.