Hello and welcome
He sounds like he has had a very happy life with you and is certainly in his twilight days.
When they age, they do eat less and sleep more. Is he manageing to groom and still go to the toilet ok?
You could offer some softer foods such as boiled egg, rice, chicken and baby food and some veg mashed up.
Personally, if he was just looking old and not in pain I'd enjoy my days with him. You have already adapted his cage for him so sounds like you are doing lots already
