They could be from the early 50s up to the 80s. Such inverse levers were
common on french bikes with flat handlebars like porteurs, city (gentleman)
or mixte bikes:
-- Dirk Feeken Heidelberg Germany
"Jon Spangler" <email@example.com>:
> I just found these "inverse-mounting" Mafac brake levers (ebay item
> #160303669327, from a French seller) while surfing.
> Does anyone have any info on how old these might be, and on which
> bikes or handlebars they would have been used?