What is self- awareness? and When does one become self aware? These are both hard questions to give an exact answer. I believe that self- awareness is when one starts to recognize their self and the environment around them. Because no one has a memory of when they became self aware, it is a hard concept to know when or why it happens.
Some research states that they believe this occurs around the 18th to 21st month in a child's life. This was determined by testing young children of their ability to recognize their self in front of a mirror. Below is a link to a video of one of these studies.
Even though there is now some research on when a child is able to recognize their self, it is still almost impossible to say how that happens. Is it something that occurs just overnight? Or is it something that slowly grows? What changes in the brain that lets this more advanced world come about? These are all questions that are nearly impossible to answer because so much is still unknown about the brain. All this unknown, though, is what makes the brain and one's consciousness and self- awareness so fascinating.