Frank Woodruff Buckles is the last living American veteran of World War I; he's now 108 years old. He was only 16 when he enlisted, but lied about his age to Army recruiters. He drove ambulances in England and France, and escorted prisoners of war back to Germany after peace came. But WWI wasn't the only conflict that hit him. According to Wikipedia:
In the 1940s Buckles worked for a shipping company in Manila, Philippines. He was captured by the Japanese in 1942 and spent the next three and a half years in the Los BaÃ±os prison camp. He became malnourished, with a weight below 100Â lb, and developed beriberi, yet led his fellow inmates in calisthenics. He was rescued on February 23, 1945.
Since the mid-50's, Buckles has been living on a 200-year-old farm in West Virginia near Shenandoah Junction. Here's a short film by Sean Dunne featuring an interview with Buckles, as he talks about his experience in World War I. The pace is slow (as you'd expect from a centenarian), but I found this little film riveting -- it's fascinating to hear what a man of such great age (and presumably at least somewhat commensurate wisdom) has to say.
Representative quote: "When I came back, the parades were all over. Nobody gave a damn. I tried to buy a pack of cigarettes; couldn't buy it -- I wasn't old enough."
See also: List of last surviving World War I veterans by country. The oldest living WWI veteran in the world is John Babcock from Canada, aged 109.