For an outfit that's casually classic and GQ-worthy, choose a navy overcoat and navy jeans. Avoid looking too casual by rounding off with a pair of black leather loafers. This ensemble illustrates that as a middle-aged man, you have a wide array of sartorial options.
If you want take your casual game to a new height, dress in a black shearling coat and navy jeans. Feeling transgressive? Jazz things up by wearing a pair of black leather loafers. Overall, a perfect example of smart casual fashion for 40-year-old gentlemen.