I think you just need the right teacher. It's true that some people (such as myself) can perceive and imitate a large variety of sounds and therefore 'sound nat

I think you just need the right teacher. It's true that some people (such as myself) can perceive and imitate a large variety of sounds and therefore 'sound native' in any language (which isn't actually indicative of true language ability in my opinion - one might just know a single phrase), but for the people who can't do this, you just need the right teacher, someone who will take the time to drill with you over and over and also provide the right type of instruction for the student (such as curriculum learning to move towards producing difficult sounds). What may be special about kids learning a language (or anything, really), is that they have no preconception of a 'correct' way to do things, including how to move their tongues. That being said, I can't whistle to this day.