Remove all items from the cedar mantle. Attach a piece of 100-grit sandpaper to the bottom of an electric sander. Run the sander along the edges of the mantle, rounding them out. This will help the mantle look older.
Fill a sturdy plastic bag with 40 screws of varying sizes. Hit the cedar mantle repeatedly with the plastic bag until the entire surface of the wood looks distressed.
Tap the mantle lightly with a hammer. This will create a few dents here and there and nicely add to the distressed look.
Lay a nail punch on the top of the mantle, and hammer it against the cedar. This will make the mantle look like a heavy piece of furniture has banged into it. Repeat this on the sides of the mantle.