My 9 year old cockatiel Ellie has arthritis in her foot/leg and wings. When she flies she has to hold her wings up because of the pain she is in. I don't know how cold it is where you are but you should put a heating pad between blankets on the cage at night. I would also recommend a vitamin supplement. Get soft perches such as cotton, it's more relaxing on their feet. Make sure you have a variety of sizes for perches so he can exercise his feet. If you notice he is having trouble getting around get some or make some ladders and wrap them so they are a solid piece (no steps) and put it across the cage so he can walk along it to his dishes.
Ellie sometimes lays in her food dish to get off her feet so I need to make a little pad for the corner so she has something to lay on.
Ellie sometimes lays in her food dish to get off her feet so I need to make a little pad for the corner so she has something to lay on.