Combining a white crew-neck sweater with a blue denim shirt is an on-point idea for a laid-back yet on-trend outfit. Add a dose of stylish casualness to by rounding off with white canvas low top sneakers. Can you see how very easy it is to look on-trend and stay comfortable when cooler weather arrives, all thanks to looks like this one? Overall, a great example of casual style for 20-year-old guys.