Cat of intermittent age ( when we got it from the RSPCA years ago, they gave it a rough age of 3 so he's about 15 now) has stopped grooming himself beyond his back legs. He got matted so took him to the vet who checked him.over and then partially shaved him. ( Bless). He's now starting to get matted again. Any advice? Ta ps he's otherwise (AFAIK since last month's vet visit), fine, eating, drinking, pooing etc. He's also v nimble for his age jumping down fences and running up and down stairs.