You may think having a bigger brain makes you smarter but the size of your brain actually doesn’t affect your minds power. Most adults have the same size brain, 3 pounds is average. The way the brain develops affects a persons intelligence. People differ in how they learn and remember as well as how quickly they learn and how well they think. Mental growth is often inherited from your parents, environment and surroundings. While most 5 year olds are learning to tie their shoes Kim Ung-Yong was learning complicated math problems and 4 languages. His parents were university professors and he had a great capacity for learning and was exposed very young. The brain stops growing in size at about age 15 years old.