When is a cat senior?
A label, not a diagnosis
The useful part of the label is planning: easier access to resources, regular examinations, and a record of appetite, weight and behavior. A birthday cannot tell you how comfortable a cat is or which tests they need. A younger-looking cat can still have an illness that is hard to see.
Compare with your own cat
Watch familiar activities: reaching a window, grooming the back, entering the litter box, greeting you, eating a meal. Write down what changed and when. Videos of movement at home can help your vet understand a change that does not happen in the exam room.
Do not file it under old age
Cornell advises contacting a veterinarian about changes in behavior or physical condition rather than assuming they are inevitable. Eating less, weight loss, new accidents or avoiding touch deserve a conversation. Bring your notes and ask what to watch between visits.