Every twenty years or so, Americans are surprised to encounter a new rising generation. They are struck by some publicized event or situation in which youth seem to behave very differently than the youth who came just before. This typically happens when the oldest members of the new generation are in their late twenties or early thirties. The average periodicity of these events is significant. At 21.5 years, it is very close to the average recent length of a phase of life—and of a generation.
