You'll be amazed at how easy it is for any gent to get dressed this way. Just a shirt jacket combined with burgundy chinos. Play down the casualness of this look by rocking oxford shoes. A wonderful example for any guy who's working out how to dress as a gentleman in his twenties.
A shirt jacket and black sweatpants are both versatile menswear staples that will integrate well within your casual arsenal. For something more on the classier end to finish off this ensemble, introduce oxford shoes to this outfit. Just because you're 20, doesn't mean you can't dress up like a gentleman, and this combo illustrates exactly that.