Well, I'll give you my story. My native language is spanish. Yet I've always had trouble "rolling the R's". When I was young, my parents thought it was just a kid's way of talking, and that I would grow up and it would go away. Well, it never did. So I spend my youth, adolescence and part of my adulthood being constantly asked "what did you say?" After I graduated from college and started working, being forced to talk to a lot of people, I got a bit more self-concious of my speech impediment. So, I started practicing. Mainly, putting the tip of my tongue on the gums behind my front teeth and trying to make a sound like a motor running (sort of), then trying to incorporate that sound into the words that needed it. It took me years, but since I was forced to practice often (I live in a Spanish-speaking country), I ended up mastering it somewhere in my late 20's. As you can see, my story might not be very encouraging, but what I'm trying to say is that it can be done. You just need A LOT of practice. Curiously enough, I find the english and the french "R" to be a lot easier. Maybe I was born in the wrong country.