For a look that's pared-down but can be dressed up or down in a myriad of different ways, team a navy dress shirt with grey plaid chinos. If you want to instantly smarten up this look with a pair of shoes, introduce oxford shoes to this outfit. When leaves change color and autumn is in the air, you'll appreciate how great this outfit is for transeasonal weather. A vivid example for any man who wonders how to dress as a gent in his 20s.
As you can see, it doesn't require that much effort for a man to look casually smart. Just wear a navy dress shirt and khaki chinos and you'll look awesome. For something more on the smart side to complete this look, introduce a pair of oxford shoes to your outfit. This one is a viable option if you're crafting a comfortable transition look. This outfit illustrates that in your twenties your dressing options are looking good.