Go for a simple yet casual and cool option by pairing a dark green long sleeve shirt and skinny jeans. If you wish to immediately elevate your outfit with one piece, why not complement your look with a pair of brown double monks? Come boiling hot summer days you're looking for a look to keep you fresh and seriously stylish –– this getup is just what you need. Those who are curious how to wear cool casual looks as you reach your 30s, you have your answer.