I need help with my old cat

Madison • God👏🏻 // single // 17

He’s about 18 years old so he’s pretty old to me lol but I would like help on knowing what kinda cat he is and also what can I do to help him cause he is so skinny and hardly eats and when he does he never gains weight and he’s been like this for about a years now and he’s blind in one eye and we feel like he’s going deaf. He would always no matter what protect our house from any other cats cause all our cats are inside and outside cats (we have 3 cats all together but they are couple years old).

He got pretty bad a couple years ago in the second picture you can see

He’s all black except his paws and nose and mouth and down his neck and down his stomach.

I’d really appreciate the help! ❤️