Maturity comes with knowledge and other things that you learn during your life (from experience and other sources). So a person might not be considered mature at the age of 14 but they could be more mature than a adult at the age of 18, because they experienced more difficult situations or things like that.
The brain is the most vital organ in the human body because they're more developed than the brains of other animals. However, humans have traits that other animals don't, such as, the ability to think, ability to invent new ideas, and ability to remember.
