Children and adult language learning differ in a number of ways. Firstly, the brain of a child is still developing whereas the adult brain is fully mature. The child’s is therefore more flexible and the neurons in the language system can adapt in accordance to both a native and a foreign language. This is why children are often able to learn a language without an accent in the speech and are able to distinguish the phonology of their second language better. Adults on the other hand, have a mature brain and are able to use their experience when learning. Adults are better and faster at learning by analogy, and at learning abstract rules and applying them. In addition to these differences in their brain capacity, children and adults typically also learn a second language in very different environments. Adults and teens learn a new language in a formal school setting, children learn by immersion e.g. in language day-care.
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In order to answer when one should learn a second language, one should first determine what one wants to optimize: the end result or time devoted to learning. As a rule of thumb, a language which is learned before the ages of 6-9 is typically learnt to a level where the speaker has no detectable accent and is very comfortable using it. However, this requires that a child spends a considerable amount of time hearing and using the novel language. On the other hand, if a language is learnt later, speakers may have a slight accent in their pronunciation but may otherwise reach a very proficient native-like level. Moreover, in proportion adults spend typically less time on the actual learning compared to small children learning a language. Of course adults can also learn a language through the environment in which case the time devoted to learning is similar to that of small children. Adults who learn this way typically nevertheless have an accent while otherwise reaching a good level. It should also be noted that while children are able to learn a language without an accent, both adults and children learn vocabulary equally well.
Especially for elderly learners the motivation to learn plays a crucial part in the quality of the outcome. In fact, even elderly people above 60 years can show good language learning results, which has been shown to also have a “protective” effect for memory diseases such as Alzheimer’s disease. Humans are naturally curious and people of all ages can be encouraged to learn languages and explore other cultures in doing so.