This combo of a navy denim jacket and a brown crew-neck t-shirt is proof that a safe off-duty look doesn't have to be boring. Add white athletic shoes to the equation to easily up the street cred of this ensemble. So as you can see here, it's a stylish, not to mention season-appropriate, getup to have in your transitional rotation. And if we're talking casual outfit ideas for gents in their thirties, this combination looks good on almost any gentleman.