The last Civil War veteran died in the 1950s so undoubtedly many World War II veterans knew a Civil War veteran. When I was a child I knew an old woman who was born in February 1869--if Lincoln had not been assassinated he would still have been President when she was born.
Back in the ‘70s I worked with a little old lady who said she came to California via Cape Horn in a sailing ship. I was in awe of the history that stood before me.
President John Tyler (b. 1790d. 1862) has, at last check, two living grandsons. Apparently it was a family tradition to have children very late in life.