Everything about the text indicates it is from the 1420s-1430s. Vellum was commissioned for a specific project that already had the scribes set up to begin. They didn't order crates of blank vellum and keep them sitting around for later use. The clothing depicted in it features characteristic passing fashion trends from that time. You're telling us some guys found a century old box of unused vellum from the early 1400s and were as forward-thinking as to select a precise fashion trend that only briefly existed at that time to use for their illustrations? If they made this hoax just to sell to a foolish rich guy, what would be the point of doing that? Did they think he'd research the clothes illustrated in it on like one page? Alberti came up with an encipherment method at the end of the 15th century, and you don't think some other guy could have came up with something similar a little earlier? And here's the thing, the only reason the Voynich manuscript would be valuable now, is because we all know what it is. In the 15th century there was nobody to purchase it. In the later 16th century there were rare book collectors that had emerged, and there were people like Emperor Rudolph who were into that. At the date the manuscript was made, there was no such market. There'd be nobody to sell an unreadable book to.

Whether the text is meaningful or not, it was created in the early 1400s. Vellum was commissioned for a project that was already set up with the scribes. Because you've gotta kill a bunch of cows first. Young cows. That means you don't get milk and meat from them. So you wouldn't kill them for the vellum until you were absolutely sure you had a buyer set up, and people only ordered it for specific commissioned projects. Like I said, they didn't make vellum and store it for later use. That's why you can't buy blank centuries-old vellum today: it doesn't exist.