The document discusses the optimal age for learning a second language, highlighting that earlier exposure (around age 3-4) enhances cognitive skills, while starting at early adolescence (11-13) can lead to better pronunciation and proficiency. Researchers agree that the ability to learn declines after puberty, and while younger children may struggle with complex linguistic skills, they display remarkable language learning capabilities. Bilingualism can lead to code-switching, which researchers suggest is a natural part of language development rather than a hindrance.