There is a critical cut-off age for learning a language fluently, according to research. If you want to have native-like knowledge of English grammar, for example, you should ideally start before age 10, say the researchers.
People remain highly skilled learners until 17 or 18, when ability tails off.
The findings, in the journal Cognition, come from an online grammar test taken by nearly 670,000 people of different ages and nationalities. The grammar quiz was posted on Facebook to get enough people to take part. Questions tested if participants could determine whether a sentence written in English, such as: "Yesterday John wanted to won the race," was grammatically correct.
Users were asked their age and how long they had been learning English, and in what setting - had they moved to an English-speaking country, for example? About 246,000 of the people who took the test had grown up speaking only English, while the rest were bi- or multilingual. The most common native languages (excluding English) were Finnish, Turkish, German, Russian and Hungarian.
Most of the people who completed the quiz were in their 20s and 30s. The youngest age was about 10 and the oldest late 70s.
When the researchers analysed the data using a computer model, the best explanation for the findings was that grammar-learning was strongest in childhood, persists into teenage years and then drops at adulthood.
