My 11 year old silver paint still looks good but it just won't hold wax like a newer paint job would. I wax the car every 3 months and that seems to be just the right amount to keep a good bead of water on it when it rains. I also go through the entire process of cleaning the paint, waxing it and then polishing it every 6 months. If the paint were newer and in really good condition I would imagine that every 6 months would be adequate. There is no single correct answer for every car. It really depends on the condition of your paint.
