If you're in search of a casual but also seriously stylish getup, consider pairing a white long sleeve shirt with olive chinos. Feeling brave today? Break up your getup by wearing a pair of black suede loafers. Stick with this one if you're searching for a solid summertime getup. Overall, a good demonstration of smart casual fashion for 40-something men.
This combination of a white long sleeve shirt and a light blue plaid long sleeve shirt will be a good illustration of your expertise in menswear styling even on lazy days. Dial up the appeal of your outfit with a pair of black suede loafers. Seeing as it's roasting hot outside, this combination seems perfect and entirely summer-friendly. This combination is probably what you're looking for as a 40-year-old gentleman.