Children with exposure under the age of 11 typically have no trouble [achieving a native-like accent] in the other hand
I started learning French at 10, and Spanish and Italian at 12, so this seems to predict I would have a native-like accent in French but not in Spanish or Italian. As a matter of fact, I do think my accent is slightly better in French, but I don't think the difference is large enough to count as "native-like" versus "non-native-like", and furthermore I suspect it has more to do with patterns of study and practice well after the ages in question (e.g. some systematic training in French phonetics at age 16) than with anything that went on in my brain during the first year.
1) Anecdotal evidence doesn't really mean anything. Everyone develops slightly differently - 11 years isn't a hard wired rule. These are rough averages. I expect that in the data there were some nine year olds that had difficulty assimilating, and some 13 year olds that had no trouble.
2) What the early exposure does is for example train your brain on distinguishing and producing phonemes which would otherwise literally be imperceptible otherwise.
3) French, Spanish, and Italian are very similar languages, in structure, idioms, and phonetics. It is not uncom...
NPR reports on a study giving volprioc acid to adults and training them on pitch (singing):
Brain plasticity is useful for a whole lot more than learning pitch. As the article notes it would be invaluable for training one's ear to pick up sounds of foreign languages, but also it seems reasonable to this commentator that high levels of plasticity during rationality training or other forms of self-development would result in more transformative results.