I am always a little bit amused by the definition of ‘old’ in the US when compared to European architecture. Having said that, one of the benefits of these different perspectives on what is old is that things considered ‘new’ and not worth preserving in Europe are considered ‘old’ in the US and are preserved.
A very good example of this is the Architecture Gallery in the Art Institute Chicago. I love that as buildings were demolished in parts of the City, art lovers rescued elements, be they windows or parts of the stonework to ensure that on replacement of the original structure, its original grandeur is not forgotten. Each of these exhibits is accompanied by a detailed story of what it was created for and how it was saved and came to be on display in the museum. I can’t tell them all and recommend you go and visit to read them yourself.