Although there have been people living in what is now the US for thousands of years, the number of technologically advanced occupants has been limited. For this reason, buildings that are over 400 years old are very rare. According to a site on Wikipedia, the oldest building in the US is a mound in St. Clair County, IL. The next oldest buildings are in the southwest, then Puerto Rico. However, there are many more extant buildings beginning with the 17th century. Many of these are from the colonial days and are located in the northeast.
Things are much different in Britain. During our travels, it was not unusual to see cathedrals, abbeys, and castles in even the smaller towns that were many hundreds of years old. Of course, some of these structures only remain as ruins while others have been renovated over the years to preserve them. Still this was quite different from what you see here in the US. In some cities, parts of the stone walls used for fortification still remain with the original gateways now having paved roads running through them. Modern day buildings blend together with made over older buildings.
In Chester, England, the old city walls were originally built by the Romans in the first century. They were extended in the twelfth century and still remain, being a big tourist attraction. Our tour guide told us that many of the cities and towns we visited were originally founded by the Romans around 2000 years ago. You just don’t hear this about cities in the US. If you do, please let me know because I want to visit.