Combining a long sleeve t-shirt with cargo pants is an on-point pick for a casual and cool look. You could perhaps get a bit experimental on the shoe front and add black leather derby shoes to the equation. This combination shows that dressing your age and looking fashionable are not mutually exclusive things.
A long sleeve t-shirt and cargo pants are great menswear elements to add to your day-to-day casual rotation. For something more on the sophisticated side to finish off this getup, introduce dark brown leather casual boots to this outfit. Semi-casual looks for stylish young gentlemen aren't actually that hard, as you see here.
Inject some fun into your daily arsenal with a long sleeve t-shirt and cargo pants. And if you need to instantly up the ante of your look with footwear, complement this ensemble with black leather loafers. This getup shows that cracking the fashion code as a 20-something guy is totally doable.