Why are you stating a hypothesis as if it was fact? I'm 30 and started learning Spanish (1,000 hours so far) and think I'll be near-native level in another 1,000 hours and maybe actually native in 5,000 total hours which I might get to by the time I'm 40. As we age, we simply have other commitments that we cannot devote this much time to language learning. Kids "easily" learn language because they can easily put 1,000 hours of exercise each year for 5 years.
I have lived in a foreign country for about 3 years. My wife is from there and I speak with her in that language every day. I also took courses until the B2 level. My communication in that language amounts to easily more than 5000hrs. I am fluent, but no native speaker would call me native and that will never happen. My wife learned my language in school since elementary school up to graduation. She lives in my country since about 5 years. In her job she has to talk to people for basically 8hrs a day in the local language. She is fluent but nobody would call her native. Instead people wonder where she is from because they cannot match her accent to a particular country. Most likely we will never have native competency in the foreign language. So if you make it to native in 5000hrs, you are way above average.
I wonder if there's some kind of plateau you reach in a learning a language that way. Like, what if you started working with a hollywood dialect coach?
I’m bilingual since a child but didn’t really use one of the languages much after age 12 to about 30. When I do speak the second language I can fool locals into thinking it’s my first language, but it takes exactly 1 mistake or mispronunciation and they ask “oh are you actually English?”. The bar is that that high for passing native fluency in another language, if you somehow could fake the accent perfectly as well (there is absolutely no way).
Yeah there's definitely a gap between functionally fluent and being mistaken for a native that requires some intentionality and effective study that is unlikely to be crossed accidentally/passively or by focusing on the wrong things/methods.
Some combination of learning the phonetics of the target language, 1000s of hours of comprehensible input, singing to music in the target language, and doing impressions of native speakers are all things that can help.
> The critical period hypothesis[1] is a theory within the field of linguistics and second language acquisition that claims a person can only achieve native-like fluency[2] in a language before a certain age.
Granted, I do admit I missed the subtlety that it applies to learning a first language as well.
