Edna, orange tabby, will be 18 next week. She's the oldest cat we've ever had and we got her at 5 weeks. Our last cat, a Siamese named Sam, made it past 16 when his liver went out. We never even kn...
Our son had two make it to 21. I'm not sure the oldest "documented" cat I've seen in practice, but it was early 20's.
They do get dementia, not as severe as in dogs in my experience. They do talk a lot as they get older, Henry is in that phase now (we really don't know how old he is, but he's a senior).