My son has a few "vintage" tour t-shirts he often wears. He also wears one with his own band's logo and one with that of the AC/DC tribute band he plays lead guitar in. He wears jeans or leather pants, doesn't have a paunch (thank god) and his hair is greying. He can be forced into a suit, occasionally, and has been known to wear a tie. Believe it or not he looks fabulous in a dinner jacket (about once every 5 years). He's 40.
The odd thing is, he never looks scruffy or out of place but then he's been a musician for over 20 years and I suppose he has "the look". Will this be acceptable in another 10 years? Heaven only knows - I'll get back to you.