Can’t be the last one, I got a great great uncle, living in a nursing home near Corpus Christi, who fought in WWI. Of course his mind is completely gone and he can barely remember whether or not he had lunch today, but he ain’t croaked off yet.
If so you need to bring it to the attention of somebody along with documentation. Everybody’s pretty much convinced this guy is the last.
You should look into it. Most claim Frank Buckles is the last surviving veteran. If you're uncle is one, too, he at least deserves some mention or notice.