Is my Piranha is sick?

I have had my red bellied piranha for about 6 months. I bought him from a couple who told me he was about 9 years old which I know is old for piranhas. He's been fine and normal until a couple days ago. Most of the red on his stomach has gone white and the area around his head and gills seems darker in patches. He is sitting very close to the top of the tank lately and moves very little. He also seems to be breathing slower than usual. Does anyone know what's going on? Is he just dying of old age, sick, or just going through a natural thing for piranhas. Thanks in advance.