If you're scouting for a relaxed casual but also stylish look, consider pairing a navy field jacket with a long sleeve shirt. Dial down the casualness of this look by slipping into burgundy leather derby shoes. Amazingly stylish, this pairing will also help any young gentleman look more mature.
A navy field jacket and a long sleeve shirt are a nice getup to keep in your current off-duty fashion mix. For a more sophisticated finish, why not complete your look with a pair of multi colored leather brogues? Ensembles like this go a long way towards maturing your style as a man in his 20s.