Technically, posters are artwork. An artist or designer came up with the print. But, if you want it to appear more like fine art, display it by itself on a wall and place a light above it like you'd see in an art gallery. This instantly makes it seem more grown-up. Remember, though, maturity is a mind set. Hanging posters doesn't make you less of an adult. But, that doesn't mean you can't make your posters look stylish.