The vellum of the Voynich Manuscript has been dated to the first part of the 15th century, though it has been noted that the text could have been written later.
The Cathars were in existence from the 12th to the early 14th centuries.
Roger Bacon, having lived in the 13th century is thus excluded from being the author of the VM.
This was the time when moveable type printing was being developed - see Wikipedia page 
There were a range of manuscript hands in use at the time - and a number of scripts (Fraktur, Latin, Greek, Cyrillic etc).
Prester John (Wikipedia page  believed to be in Africa in this period.
Early 15th century: beginning of Portuguese exploration and expansion - capture of Ceuta in 1415 .
The Wikipedia page on the 15th century is : there are links to decades and specific years.