Wear a black leather biker jacket and jeans to achieve new levels in your casual fashion game. You could perhaps get a bit experimental on the shoe front and class up this getup by rocking dark green derby shoes. All in all, an ideal demonstration of laid-back style for 30-something Millennial men.
For an outfit that's pared-down but can be worn in a multitude of different ways, wear a dark green military jacket with jeans. And if you need to easily dress up your outfit with a pair of shoes, why not add a pair of dark green derby shoes to the mix? As you can see, dressing maturely doesn't mean dressing old.