Perfect the laid-back and cool ensemble in a white and blue short sleeve shirt and brown chinos. And if you wish to instantly tone down your outfit with footwear, why not add athletic shoes to your outfit? As you can see here, this look is a really savvy pick, especially for unpredictable fall weather, when the temperature is dropping. Take cues from ensembles like this if you want to add seriousness to your 20-year-old's look.