Consider pairing a white crew-neck t-shirt with dress pants for a neat refined ensemble. And if you need to immediately dial down your look with one piece, introduce espadrilles to this getup. Just because you're 20, doesn't mean you can't dress up, and this outfit illustrates exactly that.
If the occasion calls for a polished yet killer outfit, rock a white crew-neck t-shirt with dress pants. You can get a bit experimental on the shoe front and play down this ensemble by sporting a pair of espadrilles. This is a modern and age-appropriate combination for a young man.