Language development, for instance, has a critical period that begins in infancy and ends between eight years and puberty. After this critical period closes, a person's ability to learn a second language without an accent is limited. In fact, second languages learned after the critical period are not processed in the same part of the brain as is the native tongue.
The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science (ed. Penguin UK, 2008) - ISBN: 9780141923680