Just because someone is a Jewish scholar does not make them Christian. Most jews follow Judaism, which doesn't recognize Christ. So Jewish scholars do not have to have any vested interest in making Christian followers happy. Heck, not even Biblical scholars always have an interest in that, as Bart Ehrman is technically a biblical scholar and he claims Jesus isn't God, which will piss off 100% of Bible believers.
Second, no one was talking about this before, which is why no one had to openly debunk it before. If this really has been a part of history, are you suggesting someone got the gender spectrum eradicated from history and forced everyone to go by the genders they were born as? Because who would even be able to do that? Islamic countries hate these people too and several African countries think America is stupid because we encourage this gender spectrum stuff. This didn't come from Christianity. Because people who have always hated Christians have the same opinion. If someone actually conspired to do this, they'd have to be as old as Abraham, since he had both Isaac and Ishmael, the fathers of the people who are now majority Christians and Muslims, respectively.
The age of humanity is heavily debatable, but even if you believe in the Big Bang (which scientifically makes no sense), there's not really any texts in history dating back more than 10,000 years, with the exception of the epic of Gilgamesh, which nobody thinks is real, and there certainly werent any in real time (even the Torah wasn't written in real time).
Thats not the same. Following a god is a choice. People in the Bible left God despite knowing He was real from the very beginning. Heck, the first thing man does in the Bible is disregard God.
Whereas if the first people to exist recognized more than the 2 biological genders, this would have passed down throughout the generations like belief in God did. Only there wouldn't be a reason to "stray from it" like there would be with God, since human nature is quite rebellious. To reduce the number of genders would have been a scientific argument, which could be proven right or wrong based on data. Following God was a matter of "do I want to or not?"