Some kids already know at the age of 5,6,7,8+ years or even earlier.
IA. And I think it's better for them to be "open" about it younger, because it's easier to get things "done" when you're younger, so you could transition/stop hormones. This isn't the first time too, three years ago some young transgendered kid came out, and she's like a German popstar.
I feel like this generation, like you said, people start to realize/be vocal about being "born in the wrong body", like in this episode of the Tyra show (specifically, 7 and 8)
I don't like them tacking GaGa's name onto this even if she was a help in him coming out. It makes it look like it's her doing and that she makes people be different.