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.
It might be scientifically accurate but I think the notion of an age cap is misguided. Just because it’s harder doesn’t mean it’s impossible, and the idea of an “age cap” just makes it seem like you shouldn’t even try (might just be my interpretation).
Also it’s just super helpful to learn something even though you’re not perfect.
I’ve started learning English at 10, put in a lot of work over the years, and it got to near-native in my late 20ies (certified by my language-nerd native-english-speaker wife). At 20 I had trouble booking hostel rooms over the phone.
In my 40ies now and I feel like most of the skills that make “me” today, including playing instruments, programming languages, all kinds of crafts, I learned way past ten and many of them past 20. Started learning Spanish at around 35, nowhere near native but decently conversational. About to start the next course in Catalan soon.
So, this is the one thing where I think people just should ignore the science (which is usually not my stance at all) and get cracking, you can teach an old dog new tricks, and it’s always helpful and fun.