WASHINGTON — Most Americans have never known a world where man hasn't been to the moon.

It used to be a given people knew where they were when man first walked on the moon on July 20, 1969, watching the black-and-white images on television. But now, most Americans don't know where they were because the majority of Americans hadn't been born yet.

The median age of Americans, as of last year, was 36.8, meaning more than half of U.S. residents are younger than 40, according to the U.S. Census Bureau. No figures have been calculated for this year yet.

Five years ago, when NASA celebrated the 35th anniversary of the moon landing, the median age of Americans was 36.1, so most residents were at least alive when Armstrong made his giant leap for mankind.

That changed sometime between July 2005 and July 2006, according to the Census Bureau.