Adults learn language to fluency nearly as well as children: study
I have started to ponder a hypothesis that this thing applies to almost any learning. People claim that it is easier for kids to learn, but for most of the things kids learn, they use much more time than any middle aged could in practice. Like, "ooh, look, my nephew learned backflip on a trampoline so quickly and easily, I would never learn that". Yep, he just spent hours a day on the thing for the last couple of months. You do the same and I bet backflip is not that hard.