My first generation of cat family lived to 19, 20 and 21. At the ages each of them died, I had had them for half my life (my entire adult-life). The eldest predated my wife and kids, of course I'd give them medicine when sick and take care of them, they had shared my entire adulthood with me up to that point.
Oldest of next batch of cats is 10. He was once the kitten that tormented the older cats, now he's the old cat that get tormented by the youngsters. He's an indoor cat so I fully expect him to live into his 20's too. 18lbs of fluff and muscle (part Maine Coon).