We all know about when Mantia wrote this famous solo, but in what year exactly? Here is what I found. It shows the copyright date (although he could have played it for a while before submitting for copyright).

Catalog of Copyright Entries: Musical compositions, Part 3, Volume 4, Issue 1

Quoted text:
All Those Endearing Young Chamrs; fantasia arr. by Simone Mantia, for baritone and piano.
Dixie music house, Chicago, Ill.
C 193440, Nov. 16, 1908

U.S. Government Printing Office, 1909