Wear a red gingham long sleeve shirt and black chinos to assemble an interesting and modern-looking casual ensemble. For something more on the classy side to finish off your ensemble, complete your ensemble with a pair of black leather dress boots. When it comes to dressing for unpredictable fall weather, nothing beats a neat combination that will keep you comfortable and looking your best. Ideal if you're on the lookout for some seriously inspiring smart casual style for 20-year-old gents.