Why not consider wearing a grey polo and jeans? These items are totally practical and will look awesome when married together. You can take a more polished approach with shoes and throw a pair of black leather chelsea boots into the mix. Combinations like this have a sophisticated air that befit young gentlemen very well.
This casual combination of a grey polo and jeans is a goofproof option when you need to look laid-back and cool but have no time. If you wish to instantly class up your outfit with a pair of shoes, why not throw charcoal suede desert boots in the mix? This getup is most probably exactly what you're looking for as a 30-year-old gentleman.