I mix things up with jeans, tees, polos, sport shirts, dress shirts, Hawaiian shirts...whatever happens to suit my mood and won't look out-of-place for where I'll be.
As for "age-appropriate" I would steer clear of anything that's emblazoned with the manufacturer's brand, such as Abercrombie & Fitch stuff. I think guys of any age who wear things with ostentatious labeling look like idiots. Ditto for anything tight-fitting, walking shorts higher than mid-thigh, Speedo minis, or those cheesy Crocs shoes.
Come up to DC sometime...I'd go shopping with ya.
