I’m from Vietnam. I’ve been in the UK for 10 years now. When I met my English husband 13 years ago at 19 I knew 0 English. We communicated using machine translation. So that’s when I started learning English. Fast forward to present day after immersion, living in an English speaking country, formal study, etc. and I’d say my writing and listening (understanding) are good, but my speaking and reading are still bad. I kind of gave up on trying to become fluent at this point.
Like with any other ability, like painting or playing an instrument, learning a language is something that some people can do better than others.
And while starting to learn a language as a baby or toddler has it’s advantages (Our kids basically grew up bilingual), I started learning English in school when I was 11, and I still managed to learn it. Yes, native speakers will still tell me that I have an accent, but I’m good enough that they cannot place it, just that it is not native. With only 2-3 weeks a year in the UK, it is probably the closest I can get. Written English is another matter, anyway. I’ve probably read way more English books than the average native speaker…