I was surprised that several people said they found it unusual to build a house out of wood--someone from I think Germany said that there, you only build a wooden house if you're poor or making an environmental statement. What other material do people use? Steel and concrete would be typical here for, say, a skyscraper, but do people use that for ordinary homes in other areas? Another person made the point that sound travels through wooden houses, which is a peeve of mine, so I want to know how I can build a house that's quieter! 
concrete or bricks are the most common building materials here. (Off course, here we have loads of sand and canals everywhere to easily transport sand by ship.)
Off course, with these materials houses tend to last much longer. I once read here about people thinking that a 20 year old house is getting old (for maintenance etc.) I just bought an 18 year old house, so it is still relatively new and in great condition, only the interior needed a cosmetic fix-up and the wooden window- and doorframes were badly maintained. People live in 400 year old houses here that are still in good condition (though they have often been completely upgraded on the interior to make them suitable for modern standards.)
About older houses--a lot depends on where you live and what your personal feelings about older houses are.
On the east coast, you can still find a few houses, built of wood mostly, that were built in the 1600's. Some of these are still lived in, but many have been turned into museums. The Paul Revere house in Boston is an example. There's a house in my town that was built in 1875-ish, that is part of the local historical museum.
Four hundred years for any building in the US is going to be a stretch--there simply weren't that many non-Native Americans here at that time to be building a typical European style house. (You can still see the remains of some pretty incredible adobe dwellings built by Native Americans in the southeast, though.)
In general, along the east coast, in the older cities and towns, there are plenty of houses that are 100-150 years old. Most are of wood, but in the cities, you'll find row houses of brick or stone. Think of the New York City brownstones, which appeared sometime after 1830.
My city, which has been around in one form or another since the 1650s (which is old for the US), as a lot of housing stock that is over 100 years old, which is old for us. My house was built in 1900.
There are problems in dealing with an older house--money has to be spent upgrading the plumbing, the electrical system, the heating system. More repairs have to be done on the roof, the windows, that sort of thing.
The fact is, a lot of newer houses (but not all) aren't as well constructed as the older homes. And if they aren't maintained well, they do show signs of age within 20-50 years.
Those of us who like older houses like the solid plaster walls that reduce the amount of noise that travels from room to room, the details that newer homes sometimes lack, such as nice wood trim around doors and windows, the craftsmanship that went into the older buildings.
But in many places in the US, even on the east coast, there simply aren't very many older buildings. You really have little choice but to buy a newer home. And hope that the builder did a good job on it.
