Wood shutters last a long time. No matter how much abuse your children, guests, and furniture dole out to your shutters, they don't twist or bend. It can take over 350 pounds of pressure to mar real wood pieces. Some materials can make slats only 29 inches long because the material will bend if stretched too far, but wood does not have this problem.
You can make your wooden pieces any length. Not only this, they resist damage from the sun. Just like trees, it absorbs UV rays without a problem. The wooden slats of shutters will last for generations unless you soak your shutter or burn your whole house down.