Also, it's virtually impossible to gain fluency in a script after a very young age (around 5 if I recall correctly) and verbal language isn't much better, with native fluency very rare after the age of 13-17 or so.
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.
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-...
Without fail the best speakers told me they lost their accent because they wanted to describe a huge up hill battle. Hard work, practice, and a commitment to figure out the right way to say it. Plus loads and loads of English TV.