Brain maturation: The last section to connect is the frontal lobe, responsible for cognitive processes such as reasoning, planning, and judgment. Normally this mental merger is not completed until somewhere between ages 25 and
ANATOMY: Anatomical Chart of the Brain. Did you know that the brain makes up about of a human's body weight? The cerebrum alone makes up of the brain's weight! The human brain is largest brain of all vertebrates relative to body size.