Why not dress in a long sleeve t-shirt and chinos? Both items are super functional and will look good paired together. If you're not sure how to dress as a 20-year-old man, this combination is a surefire option.
Chinos with Long Sleeve T-Shirt Casual Outfits In Their 20s
For something on the off-duty side, test drive this combination of a long sleeve t-shirt and chinos. Overall, perfect for a 20-something.