Information on the science behind learning a new language.
Best learned at a young age.
Research has proven that learning a different language is easiest learned when at a young age due to the lack knowledge about language. Example: If a 4 year old is raised around two different languages than it is most likely to pick up on both languages rather than just one.
Harder to learn when at on older age.
It also has been proven that learning at an older age is harder than learning when young. Say a 30 year old man wants to learn spanish. It will be more difficult because he already has prior knowledge of one language and will be more difficult to learn a second. Unlike a newborn, he will revert to his first language when trying to learn a new one.
How long does it take to fully learn a new language?
The average time it takes to fully acquire a new language is from 4-10 years. This is to be able to speak, read, and write that language fluently.