Why not opt for a crew-neck t-shirt and black jeans? Both items are totally comfortable and look amazing paired together. With shoes, you could go down the casual route with black high top sneakers. Think it's hard for mature guys to perfect cool casual style? This combination will prove you otherwise.
Go for a pared down but casually dapper option in a crew-neck t-shirt and charcoal jeans. And if you wish to easily dress down your look with a pair of shoes, complete your look with a pair of black high top sneakers. Those who wonder whether you can still rock cool off-duty looks as you head into your 40s, you have your answer.