Go for a white dress shirt and a grey suit for seriously classic attire. Get a bit experimental in the footwear department and dress down your getup by sporting a pair of navy leather low top sneakers. As you're moving from your 20s to your 30s, you probably want to start dressing like an adult. In this case, getups like this are perfect as inspiration.
This combination of a white dress shirt and grey wool chinos exudes class and sophistication. Navy leather low top sneakers will bring a touch of stylish nonchalance to an otherwise standard ensemble. This combination illustrates that in your 20s your styling options are pretty much limitless.
If the dress code calls for an effortlessly neat outfit, marry a white dress shirt with navy chinos. For something more on the casual and cool end to finish this getup, add a pair of navy leather low top sneakers to the equation. This pairing should erase any doubts you had about wearing more mature clothes as a man in his twenties.