http://www.oldcardboard.com/t/t206/I...al-edition.pdf
In the above article by Scot Reader it indicates that for young boys it was happening as early as 1909. On page 15-16 of the above PDF it references an article in a 1909 article “The Small Boy’s Mania" in which it talks about young boys buying packs of cigarettes to obtain the cards then the would peddle the cigarettes.
The entire PDF was an interesting read, but the article was very interesting when I ran across it a while back.