Exterior Plywood is designed to be exposed to the elements, so you can expect it to last for a long time. If you take good care of it, it should last for decades. Even if the plywood is exposed to the elements 24 hours a day, seven days a week, it should still last for at least ten years. If you are concerned about the plywood getting damaged by water, you can cover the wood with paint or another type of sealant. Paint is not as effective at protecting the wood from water, but it will keep the plywood looking good for many years.