A mantel adds visual interest and style around a fireplace that may otherwise be somewhat nondescript. Some new mantels are styled after those made many years ago, as the look is a bit classic and timeless. The downside to a new mantel is it may look too new once it's set in place. Add decades to its appearance with faux finishing or distressing techniques and supplies from a local home improvement store.
Beating the mantel up a bit is called "distressing." Distressing in this case isn't a situation that causes worry; it's a means of adding artificial wear to that mantel to make it look like it's far older than it really is. Add the impression of years onto that mantel by beating sharp corners in random places with a hammer, using the side, claw and even handle of the hammer too, for variation. A bag of nuts and bolts swung onto corners of the mantel bears similar effect.
Removing wood doesn't mean dismantling the mantel; it's part of the distressing process. Drill small holes clustered near one another to give the effect of worms that have burrowed into the wood. Don't overdo it or it can look unnatural. Sand areas that would experience wear naturally over time, such as corners of the shelf, using fine- or medium-grit sanding block.
If the mantel looks like varnished or sealed wood rather than painted wood, rubbing a stain or glaze over the surface adds a little darkness to the appearance, as if the wood finish has aged. Sand the surface a little to help the stain soak in better, than rub on a dark wood stain with a rag. Rub more of it into areas with dents or cracks, as this will make them more visible, enhancing the aged appearance. Wipe most of the stain off, working quickly to avoid making the mantel too dark. A watered-down dark latex or acrylic paint can be used instead of stain for the same effect.
Add the look of years to the mantel by painting in various shades, with a coating of wax in between. For example, paint it a dark red color, then rub candle wax over it after the paint dries. The wax helps the paint come off more easily for the aging process. Apply a second color, such as antique white, then more wax after that dries, followed by a third color. When completely dry, sand away areas of the paint that would normally receive the most wear, such as the top and corners of the mantel shelf and sharp edges along the sides or near the opening of the fireplace. Sanding reveals the various colors underneath, as if the mantel was painted many times over a span of decades.