On average, it takes 1,765 hours of learning for a person to become fluent in English. The amount of time required for a person to become fluent may be shorter for a learner whose native language is similar to English.
Contrary to popular belief, there is no positive correlation between a person's youth and the ease with which that person is able to learn a second language. In fact, under controlled conditions, the opposite is true; older children tend to be more successful language learners than younger children, and adults tend to be even more successful.
Factors such as the lower level of proficiency required by children to communicate effectively with their peers are thought to be responsible for the misconception that it is more difficult for an adult to learn a new language.