Where do you stand on the regular wearing of concert shirts?

I used to always have my Iron Maiden shirts in my wardrobe rotation, but being in my mid-50s, I must admit that I feel a tad foolish wearing concert shirts out doing day-to-day stuff. Is there a certain age when you stopped, or are you all whatever?

(It doesn't help that concert shirts never seem to be available in "old fat bastard" sizes.)