You need to get this under control. The long haired cats will need to have their hair trimmed. Shorter hair cats, maybe not but both hair lenghts will end up getting knots and gross poo-encrusted dingleberries. You will even see the cat drag its ass across carpet in an effort to scratch the swamp ass.
Diet and exercise work and dont really mater the age. We have two cats, one is good about self regulation and the other is ridiculous and food driven. Before I got to know the extent of his food madness, I purchased a bag of cat food and brought it home. Left it on the kitchen floor absentmindedly. We left the house and were gone for not even an hour. The cat had smelled the food, ripped open the thick paper bag and began munching. Ate almost 10 pounds of food in an hour!!!! When we got home, he was bloated and his abdomen was distended. He could barely move. He really looked like those huge snakes that swallow a gazelle and then have to lay around while they digest it.
The problem with this fat cat is that he is so handsome and knows it too. Everyone who meets him wants to feed him. We let him outside and we know he goes to the neighbors and gets fed there. He has no fear for asking for food from strangers and would have no struggles in surviving if ever left on his own. So our solution was to keep him inside and highly regulate his diet. That is the only solution. Play with the cat to exercise him too.