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> There is one major disadvantage that adults have though, and that's at acquiring correct pronunciation. I think I've never met a person in my life who didn't learn a language from a very young age and who didn't sound slightly off to a native speaker.
I think an adult working full-time on their pronunciation would get within the native range of variation fairly quickly. Even native speakers only adjust their accent very slowly after moving to a new area, but accent coaches can speed up that process a lot. It's just that it involves a lot of tedious practice consciously controlling your tongue when you'd rather just speak freely and have your subconscious take care of tongue movement. So most people who do that are actors or public speakers, for whom pronunciation matters a great deal. The average language learner has better things to do...