From contextual clues, I would guess this was written pre-WWII.
I think you may be right. If this is related to my comment above about whether the author would have seen metal as 'Romanticist', I meant it in the following sense: given his musical acuity, would he have been able to see what we see in it, i.e. recognize that the harsh vocals, distortion, dissonance, melody and rhythm are part of what makes metal music both 'Romanticist' and anti-pop, but that at its core, it is a representation of a certain ideological and cultural ideal - one which is in part inspired by the Classical/Romanticist masters.
Also, when I said 'late 1900s', I wasn't necessarily excluding 1950s-onwards from that. However it would have been clearer to just to say post-WWI.
If you're just mentioning it as a statement of fact, then kindly ignore what I have typed above:-)