An adult cat, or near-adult cat, would probably be better for them, especially one that has already had some training.
I still have my doubts whether them getting a second cat is really the right idea for them, though. I mean, I love cats myself and there are two in my own household, but I know owners taking in more cats than they can handle at any one time is how you get abandoned or abused cats, and who wants that?
An adult cat, or near-adult cat, would probably be better for them, especially one that has already had some training.
I still have my doubts whether them getting a second cat is really the right idea for them, though. I mean, I love cats myself and there are two in my own household, but I know owners taking in more cats than they can handle at any one time is how you get abandoned or abused cats, and who wants that?