This is solid proof that a dark brown plaid long sleeve shirt and navy jeans look awesome when combined together in an off-duty look. For maximum fashion points, introduce brown suede casual boots to the equation. Keep this getup in mind come warmer days, and rest assured, you'll save a ton of time getting ready on more than one morning. As a 30-year-old, you want to start dressing like a grown man. If that's the case, combinations like this are ideal as inspiration.