It’s entirely up to you whether you feed your cat wet or dry food. A benefit of wet food is that it contains more moisture - 75% to 78%.
Canned food is also the best food for diabetic cats. This is because it’s high in protein and moisture and low in carbohydrates.
You should always speak to your vet though, to determine the best diet for a cat with diabetes.
If you choose dry food one benefit for you is that it is often cheaper - so will help to keep costs down, whether you choose to feed it exclusively or as a combination with wet food.
You do need to look out for a AAFCO complete and balanced statement. This means the food has the right balance of protein, fat, vitamins and minerals.
Firstly, you need to look for food that is labeled for kittens. They need different nutrients to adult cats and that will be found in the food that is specifically formulated for them.
A senior cat is considered over 11 years old. Senior cats require the same nutrients as an adult cat - with some added extras such as omega-3 fatty acids.
Make sure you are buying food that is specifically labeled for seniors (and AAFCO complete and balanced).