I've got some early 20th C. catalogues on my desk at the moment, so here 
goes.

1902 Sears Roebuck + Co facsimile
Lists mining and forestry boots.  Neither mention steel caps, and you'd 
imagine them to be early adopters of anti-toe severing technology.  Nearest 
is the mining boot with 'a heavy iron toe plate'.

Boot section omitted in 1908 SRCo facsimile

1923 Anthony Horderns Catlogue [Sydney-based]
Small shoe section with work boots.  None identified as steel capped or 
similar.

These seem reasonably comprehesnive and the steel toe would be a specific 
selling feature, so I'd expect 1923 to be a reliable terminus post quem.

cheers

Denis