If you actually look up LGBTQ+ history you can find that there were non-binary people even back in 400 B.C.

Another thing I found from quick Googling was that there was a man - James Clifford Shupe who was born in 1963 and was also non-binary. He was the first person to legally obtain an identity of being non-binary back in 2016. Which obviously isn't that long ago. It takes a while for someone to understand a concept that is unfamiliar to them, which is why racism is still a thing.

Non-binary is just something to label yourself as. It doesn't matter if you're female or male, an adult or a child. You just express yourself in ways that make you non-binary.

Some people do use LGBTQ+ terms, labels, genders, etc. to put up an act and gain popularity. Just like some groups of the BLM movement that participate in store raiding, assaulting police officers and people, people who claim to be something that they're not to gain popularity do harm for the rest of the community. That's when people like you start thinking that majority of non-binary people are just teenage girls who don't know what they are and what they want. Honestly, it's just sad that different genders, sexualities and races bother some people as it's just what people identify themselves with. The only reason it's so "new" is because in history people who identified themselves as LGBTQ+ either hid themselves from the public or were hidden. Or even worse - they were murdered. It's really not a new concept at all.