As you can see, looking casually sleek doesn't take that much effort. Just consider wearing a navy overcoat and dark green chinos and you'll look amazing. Add a fun feel to by finishing with white and blue athletic shoes. All in all, semi-formal and also age-appropriate.
Try pairing a black puffer jacket with dark green chinos to look sophisticated but not particularly formal. If you wish to effortlessly play down this ensemble with footwear, introduce white and blue athletic shoes to the equation. A great illustration for any gent who's not sure how to dress maturely as a 30-year-old guy.