Strictly extrapolating from human medicine, it is not that common for iron levels to be an issue for males or non-menstruating females unless there is some malabsorption syndrome or source of blood loss going on. When aging red blood cells are destroyed we have pretty efficient mechanisms for salvaging the iron in the hemoglobin.
However, maybe the cat does have some sort of dietary deficiency. Obviously, I am just musing as I have zero knowledge about what is happening with this kitty.