If you're after a casual yet sharp outfit, go for a short sleeve shirt and grey chinos. Dark brown oxford shoes are an effective way to infuse a dose of polish into your getup. This pairing illustrates that as a gentleman in his 40s, you have a wide range of sartorial options.
A short sleeve shirt and dark green chinos are styled to perfection here. Get a bit experimental when it comes to footwear and smarten up this getup by finishing with dark brown oxford shoes. This combo is probably what you're looking for as a 40-something gentleman.