How long do cats live i wonder?

My cat is really old and I wonder if cats out live dogs because she has out lived alot of dogs we had. and she out lived our other cat who passed last summer. She was sick or something last week . I noticed she couldn't hardly stand up to walk . but the first thing i noticed she wasn't coming to the door and meowing for me to let her inside like she normally does. then i went to find her and she could hardly walk so i end taking her to the vet. He gave her a shot of steroids or something and gave me more shots to give her at home. so now she is much better and doing good and i am so thankful! he said she may live for one more year. I wish she could live longer though. she is special to me because she belonged to my daughter who passed at age 16 in 1996 . so i feel I have a special bond with her so that's why i want to keep her around as long as possible. its gonna be hard to let her go . but I know she is just so old bless her little heart. she is a calico cat and so pretty. and even my spouse said she's not like other cats! She is so different and smart too. well i don't want another cat it hurts to loose one. and we have decided we don't want anymore pets when all of ours is gone. My spouse saids I don't need any more cause I take it hard when I loose one. he doesn't like to see me cry so much and be so upset after loosing one. but i think its better to have loved them then not to have loved them at all. anyway, just wondering what is the Life Span of cats? thanks for reading this and if you have any ideal as I forgot to ask the vet ! i was more concerned for her well being at the time .