Whatever its age, your cat will need regular attention from a veterinarian. Everyone in the family should realize that cats need medical care throughout their lives. All cats should be vaccinated against rabies and a host of feline diseases -- even if they will be staying inside. After all, Kitty might get out, or people might bring viruses in on their clothes or shoes. Even if your cat seems healthy, she should have a routine exam at least once a year.
Clean the litter box well to help fight internal parasites. Remove litter regularly, and wash the box with soap and water once a week. Wash Kitty's bed in hot soapy water and vacuum carpets to help fight fleas. Ask your vet to recommend flea remedies.
Unless you have a purebred cat that you intend to breed, you should have your cat spayed or neutered. Spaying prevents pregnancy and usually makes a female cat more relaxed and affectionate with her people, while neutering helps curtail a tomcat's desire to roam. It's best to neuter a male cat when he is between six and 10 months. If you wait too long, he may have developed that annoying habit of spraying things in the house with urine to claim them as his own.