Once they reach that age, making significant lifestyle changes isn’t a good idea.
Cats really do have nine lives, though, and are notoriously fickle. When one of my relatives died, I took his 20-year-old cat from another state to live with us, and thought the cat would die from the stress within weeks. But the cat lived another two additional years! He got a lot of love and had it really good in our house -- fresh mozzarella and pepperoni, real chicken, McDouble burgers, spring water in his bowl, lots of birds outside the window, wall to wall carpet throughout... so I guess he didn't want to miss out!
I did take him about two weeks to come out of hiding and mourning, though. Once out, he was the boss.