I've owned my cat for about 8/9 years but for the past 3 years he lived with my PIL as we couldn't have him in our rented accomodation. Now just moved and have cat back.
He was a rescue cat so don't know exact age but think he is around 15yo. He was always quite a big muscular cat but you had to monitor him closely as he will not stop eating and will steal any food not nailed down (even to the point of going through bins) so he can easily get overweight - but is perfectly healthy weight at the moment.
He went to vets other day as has injured his leg and they said he seems to have muscle wastage in his back legs - maybe related to the growing stiffness in his legs which we thought might be down to age. He can't jump/climb as well as he used to.
He can't have dried food as he doesn't drink enough and has also had a blocked bladder before (came very close to death) so we need to be careful. He is also not that fond of chewing 
I have always been fussy with what I feed him and have never found a wet food I am happy with (I am not paying good money for ash and waste products plus I wouldn't feed my kids pot noodles everyday so I won't feed my cat the feline equivilent). When we previously had him he was fed a diet of fish (mostly tinned or prawns, sometimes fresh e.g. sardines or salmon) plus bits of meat. However PIL started feeding him wet food pouches plus dried food on top and have left behind a stash. I did not know this and having read the ingrediants (4% chicken with the rest being animal and plant derivitives i.e. waste products, only 11% protein content) I am not happy to continue with this.
I've done some research as he is getting old and I want to make sure he gets a good diet and as far as I can tell:
- cats are complete carnivores and can't properly digest plant matter (which was what I thought)
- need a diet of at least 20% protein
- the two things you really need to watch out for are taurine and arginine which they can't make themselves but that are present in beef/pork/poultry and seafood/fish.
- they also need calcium - usually gained through bones (I thought maybe tinned sardines/pilchards etc in oil with the bones left in as I think anything bigger he may choke on)
- I have got a bottle of cod liver oil for him (because of the stiffness) and have checked dosage online as 1/4 teaspoon twice a week.
Food needs to be relatively soft due to chewing issues. I poached some salmon today for him and he wolfed that down for dinner, even though it had antibiotics/painkillers mixed in.
So far my plan is:
2 meals a day/14 meals a week
Tinned fish with bones (in oil not brine) at least 6 meals a week
Then selection from:
Minced turkey
Slow cooked beef (I can seperate some out from our dinner)
Chicken legs, poached and diced (butcher does them cheap)
Salmon, poached
Slow cooked pork (if I cook some for us)
Any advice or comments?