The FAQ you linked is not a well rounded source. It's referring to a very specific topic. There is a difference between language acquisition and language learning. Children have an advantage when it comes to language acquisition and older learners have the advantage for language learning.

Basically, it becomes too late to 'naturally' acquire language skills but it is never too late to learn a new language. That being said, there are some edge cases from language to language that can be a barrier to becoming native speaker equivalent in a given language as an adult learner. My battle has been shi vs. sshi in Korean. I'm aware that this exists, but I haven't been able to distinguish it in speaking or listening.