Every time I leave a sock on the floor, Sput gets it and drags it around....she's petite, so it's hard to walk with it... and yowls. She's eighteen also, this month... this week, actually, and that's been going on for a year or two.
But she's happy and doing well on her kidney diet "pig bits" and 100 mls of LRS a day, plus an herbal thing I put her on for her hyperthyroid. More chipper on that (though not as chubby) than on the prescription. She's actually playing now and then, which just makes me so happy.
My dad's cat was in his early twenties when he went. I'd honestly have put him down sooner, I think, but he and dad were a couple of stubborn old coots and neither wanted to leave the other. He did get senile and his kidneys were not great. He did not respond well to the ringers.
I have heard of cats going on into their 30s, but have never met one. Pretty rare. Fifteen is life expectancy, anything after is gravy, and eighteen is a pretty common age for cats to get to but also to leave at, in my experience.