[HAL9000Ti]

Source please, and define fluency.

I learned english at 22, german at 25, and mandarin at 28, It took several years of daily studying for each language, but I did it, and I was able to use these languages in professional environments. Plenty of people do it in my experience.

[vinay427]

I did state "native fluency" which is more descriptive.

Anyway, sure, here's a source I found quickly which actually makes stronger claims than I did: https://www.scientificamerican.com/article/at-what-age-does-...