I know someone (born in 1951) who said they remember a school announcement that the last Civil War soldier died. That matches what you had heard.

WW2 ended 75 years ago, so someone 16 serving in 1945 would be 91 today.

If I remember correctly the "why we fight" series of WW2 propaganda films opens with elderly American Civil War veterans participating in the 1940 Washington DC memorial day parade.