Approximately two million Americans served in World War I. These are the original Veteran’s Day vets. Although no one knows the exact number, the VA estimates that only between 30 and 50 of them are still alive.
More interesting information from the link:
Estimated number of war-era veterans, including those outside of war zones, in civilian life as of September 30, 2005:
World War I: fewer than 50.
World War II: 3.526 million.
Korean War: 3.257 million.
Vietnam War: 8.055 million.
Desert Shield/Storm (theater only): 615,000.
Iraq/Afghanistan (theater only): 433,000.
And:
Other wars and the ages of their last veterans the year they died: the War of 1812, 105, 1905; the Indian Wars, 101, 1973; the Mexican War, 98, 1929; the Civil War, 112, 1958; and the Spanish-American War, 106, 1992.
These old vets have sure witnessed a lot of changes during their lifetimes.