If the setting allows an off-duty outfit, you can wear a long sleeve shirt and skinny jeans. Let your styling chops truly shine by rounding off this getup with a pair of white print low top sneakers. When sunny days set in you want to feel comfortable and sharp –– this ensemble is just what you need. And if we're talking casual dressing ideas for 20-year-old guys, this getup looks cool on almost any gent.