As my GC got older, they developed spine problems & could no longer swim properly. Swimming on the surface & in circles was common. I have read that electro fishing can damage the spine of older GC if they get in the current path. My understanding that 12 years & above is a ripe old age. They will most likely soon be swimming in the grand old pond in the sky. In the past I have tried to ladder the GC age wise in the pond, every 5-6 years put just a couple of young ones in.