Only One Left

The Army Times has an article posted about the last living veteran of World War One. Out of over 4,700,000 Americans who served, he's the only one left. Interestingly enough, he also fought in the Second World War, spending three years as a POW in the Philippines. His name is Frank Buckles, and he lives in West Virginia today. Sadly, the number of living veterans of WWII are also dwindling in number as the years pass by. How long will it be until there is only one left?