This theory suggests that there's a window of time during early childhood when the brain is most receptive to learning language. After this window closes, it becomes significantly more difficult, if not impossible, to acquire language with native-like fluency.
It's important to note that the critical period hypothesis is still debated in linguistics and cognitive science. While there's evidence supporting it, the exact age range and its implications for language learning are not fully understood.
Some experts believe the critical period is more of a sensitive period, where language acquisition is easier and more effective, but not impossible outside of it. However, the general consensus is that early exposure to language is crucial for developing language skills fully.