As of July 4, 2014, the United States of America is 238 years old. The Declaration of Independence was approved by the thirteen colonies on July 4, 1776, at which point the United States became a country.
The colonies were part of the British Empire until they declared their independence. There were many people living in America before it became the United States. The first Native Americans are believed to have migrated to America as early as 30,000 years ago. It is unknown how they came to America, although one theory involves travel over a land bridge between Siberia and Alaska during the last ice age.