Make a white plaid long sleeve shirt and light blue jeans your outfit choice, if you prefer to dress for comfort without looking like a slob to look stylish. Avoid looking too casual by rounding off with a pair of black leather chelsea boots. So as you can see here, it's a cool, not to mention season-appropriate, getup to keep in your transitional rotation. Casual combinations for 20-year-old guys aren't actually that hard, as you can see here.