17 is a grand age!! Good for you for getting your baby to this great time in his life. Kidney disease is very common in older cats. If he will only eat dry food, then the prescription food maybe your best choice only because the last thing we want is for him to stop eating. If he will eat/drink it, homemade chicken broth will be a great source of moisture – which is vital when the kidneys fail. Your goal at this point is to keep the fluids going in, as too many are going out. Cats are notorious for not drinking enough, so let’s help if he’ll take it. If he’ll eat canned, excellent, make it soupy by adding water or homemade broth. You don’t want to use store broth – the salt and msg will make the kidney issue worse.
If you have other cats who are younger, now is the time to start thinking about them too, before there is a health concern. Love him all you can – each day is a blessing.