How big is a 12 year old brain?

A 12-year-old's brain is typically about 90-95% of the size of an adult brain. By this age, the brain has undergone significant growth and maturation, particularly in areas responsible for reasoning, decision-making, and emotional regulation. While size is important, the development of neural connections and pathways is crucial for cognitive abilities at this stage. Overall, a 12-year-old's brain is well on its way to reaching full adult functionality.