I built this shelf 15 years ago or so and it ended up stored on a shelf in my garage. It was originally built un-distressed, however I feel the distressing gives it a bit more character. So, give your 13 year old son and his spend the weekend buddies the right tools and you get a distressed shelf. To get it this way, I first lightly sanded the original polyurethane coat with 220 grit, then we distressed it, then we painted on a Van Dyke Brown glaze, letting that sit about 5-7 minutes, then wiping off, being careful to leave it in the indentations. A few days later it was time to clear coat with Deft. First coat, then lightly use 0000 (4 ought) steel wool to knock off raised areas, then another coat. Very fast and simple as Deft dries quickly. Next it will hang in my bathroom, ready for all the crap on the back of the toilet.
This is a close up of the worm wood look achieved by using a nasty looking tool made from a one foot length of wood with 3 Sheetrock screws driven through it. Use screws vs. nails as nails leave a square hole from the point (or at least cut the point off).