I remember I read an article about learning as an adult where the author clarifies why learning a foreign language as an adult is different to when you learn as a child. Please notice that the author said 'different' not hard. The point is that when you are growing your hearing as well as your speaking is adapting to the sounds surrounding you, to identify and imitate the sounds people do when they speak. In some sense, they were limited to familiar sounds.  Nonetheless, that doesn't mean we cannot identify and imitate new sounds, i.e. those within a foreign language but absent in your mother one. However, the process is different. When you learn as an adult, you frequently allow your consciousness inhibit the learning process which had to be natural. That's the disparity.