It's kind of odd, because many of our best museums are free to enter such as British Museum, National Gallery, Victoria and Albert, Tate Modern to name a few, yet a lot of other buildings charge an entrance fee. I went to Utah and Denver Capitol state buildings last year, and was pleased to find they're all free to enter, plus the decor inside was very impressive.
I get what you mean about buildings being very young in America. I remember I was on a city tour in New York many years ago, when the tour guide introduced us to a 200 year old building, there were a lot of oh's and ah's from the American tourist, fascinated by its age and history 😊