How does the age at which you start learning a second language impact fluency and accent acquisition?

Understanding the critical periods for language acquisition can shed light on why some individuals seem to adopt new languages seamlessly while others struggle. Research in psycholinguistics suggests that there may be "sensitive periods" during childhood where the brain is especially receptive to learning new languages, resulting in more native-like fluency and accent. This question invites exploration into the cognitive and neurological factors that influence language learning success at different ages, and whether early exposure provides significant advantages over learning a language in adolescence or adulthood.