Uncle Buddy at Age 15

This morning Uncle Buddy wanted to be blipped even though he was in an odd position after washing. His eyes and attentiveness are fine and bright. Yet, it was only when I uploaded this photo that I see how gaunt his boney body looks.
He is so skinny that it is hard for me to run my hand across his protruding spine and pelvic bones. I have been offering his food whenever he asks for it -- several times a day. And his appetite seems good enough even if he does not finish the food.
A worry for me. 
His recent visit to the vet and his blood tests indicate his condition is "good and normal" but he loses weight and the fur on his underparts is only slowly returning.
His whiskers have gone completely white now giving him a dignified appearance, I think.