Cats, like humans, live longer nowadays. If they avoid dangerous infections and fatal disorders, and do not get run over by cars, they can often reach the age of fifteen. A few with super survivor genes, get past the age of twenty and the occasional cat may even pass its third decade. A cat aged twenty is more or less the equivalent of a ninety year old human.
If you want your cat to survive into old age, then vaccination is essential if it is allowed out of the house. It is now possible to vaccinate against feline leukaemia as well as cat flu and feline panleucopaenia, a kind of viral gastroenteritis. There is also a vaccine against chlamydia that is useful if your cat lives in an area full of disease-ridden strays. If you are a cat rescuer likely to have stray cats passing through your house on the way to a rescue shelter, your own cats should be protected by chlamydia vaccinations.