Sebastian Stan moved to the US when he was 12, I think. His Romanian is passable, but not amazing (besides the obvious access, his grammar is probably at middle

Sebastian Stan moved to the US when he was 12, I think. His Romanian is passable, but not amazing (besides the obvious access, his grammar is probably at middle school level). So yeah, you can lose your native tongue if you're no longer massively exposed to if after 20-25, I think. And even in that case, you'll probably fall behind a lot after a few decades of 0 exposure and massive exposure of another language.