Parents often hear the warning: “If your child doesn’t learn a second language early, they’ll never be fluent.” Adults, meanwhile, are told: “It’s just too late for you to learn now.” These claims are familiar and tidy, but misleading. Are they actually true? Is it better to learn a second language as a child or as an adult? The short answer is that it depends on what we mean by “better.”

Much of the belief that “younger is better” comes from research on sensitive periods in brain development (Granena and Long, 2016). During childhood, the brain is especially adaptable to language input. Young children absorb sounds, rhythms, and grammatical patterns with little conscious effort, often without explicit instruction. They learn implicitly, through immersion, exposure, and everyday interaction.

This is why children who are exposed to a second language early are more likely to develop a near-native accent. Pronunciation appears to be especially time-sensitive. Once the brain becomes tuned to the sound system of a first language, usually by late childhood, it’s much harder to unlearn those patterns. As a result, adults often carry the phonological fingerprints of their first language for life.

Children also tend to be fearless communicators. They’re willing to babble, guess, and make mistakes without embarrassment. Adults, by contrast, are often more cautious. They know when they sound “wrong,” and this........

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