I don't disagree with what you are saying, but I think you are taking it a bit far. There are other factors to why kids are more interesting stories. There is additional conflict with school policies, there is the additional hardship parents face, and there is the whole phase vs real/how young is too young debate. It all makes for stories on trans kids having more news value. But while they get the most attention, it's not as if they get all of it. I remember when Kristen Beck got a lot of screen time on CNN for like an entire week. And even though it has been a fake trans person, Transparent has been getting a lot of attention with an older character. And in the art scene, Zackary Drucker has gained a lot of notoriety even though she never changed her name. I know that while these examples will never pass as cis they are still going for that archetype, and I know that there is not going to be any non-binary love in the media anytime soon, I think we'l get there eventually.