I got my first Threadless t-shirt back in 2005. It was a while before I saw anyone else wearing one. As time went by, I saw more and more people wearing them: usually people in their teens or 20s.
Recently, I’ve started to see Threadless shirts on people like me: parents, and not always particularly young parents. The photo is of a people who’s very much like me, wearing his favorite t-shirt: Patchwork. By the way, I ensured that I am not the oldest wearer of Threadless shirts by buying some for my dad.