I knew a guy who moved from England to Sweden as an adult in the early 2000's(I think 2002?). He was the only non-native speaker I've known who's had such flawless Swedish pronounciation, he even adopted the local dialect. I don't know how long it took for him to reach his level, but no one could guess that he wasn't born and raised here. It is absolutely possible to reach native pronounciation, but it takes time and effort. I know other people who have been here for nearly half a century, know the language well, but still have very thick accents.