The last surviving veteran of the Crimean War was
Rookes Evelyn Bell Crompton. He died in 1940 so my grandparents could have met him.
Actually, his article is worth a click as he had an interesting life. He later became an industrialist and electrical engineer, and did the early work on the National Grid in the 1920's. He was a president of the IEE, an enthusiastic cyclist and a founder member of the Royal Automobile Club. I get the strong impression of one of those people who are enthusiastically fascinated by everything novel they come across. Generally, such people are very good to know.
Back to my point. It's theoretically possible he could have met, as a young man, the last veterans of the American Revolution - the last British veteran is more likely, unfortunately
this only concerns itself with the last American veterans. It takes only two more degrees of separation to take us to William Hiseland, the last survivor of the English Civil War, who was in the Royalist army at the Battle of Edgehill. Hiseland could have known somebody who saw William Shakespeare on stage.
You get the idea - this six-degrees of separation thing does seem to work awfully well across time, as well as space.