For a cool and casual outfit, dress in a grey plaid flannel long sleeve shirt and a black print crew-neck t-shirt — these items work beautifully together. Infuse a more laid-back aesthetic into your ensemble by finishing off with a pair of white leather high top sneakers. A great summer wear, you can wear a variation of this getup throughout the season. If you often wonder how to dress as a 20-year-old, this combo is a good illustration.