Why does my 16 year old cat keep throwing up?

A 6 year old cat is not an old cat so it is not age that plays a factor. If your cat is vomiting a lot, make sure it's food is not old and is the right amount. If thins is fine, make sure it is getting enough hydration and nutrition. Take your cat to the veterinarian to make sure your cat is fine. Vomiting can be because of an upset stomach, which passes by most of the time. Just to be sure, take your cat to the vet.