section_path: Causes and factors/Age
section_name: Age
paragraph_text: Age
  
  Infants are limited in their ability to interpret their surroundings shortly after birth. Object permanence and understanding of motion typically develop within the first six months of an infant's life, though the specific cognitive processes are not understood. The ability to mentally categorize different concepts and objects that they perceive also develops within the first year. Infants are quickly able to discern their body from their surroundings and often take interest in their own limbs or actions they cause by two months of age.
  
  Infants practice imitation of other individuals to engage socially and learn new behaviors. In young infants, this involves imitating facial expressions, and imitation of tool use takes place within the first year. Communication develops over the first year, and infants begin using gestures to communicate intention around nine to ten months of age. Verbal communication develops more gradually, taking form during the second year of age.
  
  Children develop fine motor skills shortly after infancy, in the range of three to six years of age, allowing them to engage in behaviors using the hands and eye–hand coordination and perform basic activities of self sufficiency. Children begin expressing more complex emotions in the three- to six-year-old range, including humor, empathy, and altruism, as well engaging in creativity and inquiry. Aggressive behaviors also become varied at this age as children engage in increased physical aggression before learning to favor diplomacy over aggression. Children at this age can express themselves using language with basic grammar.
  
  As children grow older, they develop emotional intelligence. Young children engage in basic social behaviors with peers, typically forming friendships centered on play with individuals of the same age and gender. Behaviors of young children are centered around play, which allows them to practice physical, cognitive, and social behaviors. Basic self-concept first develops as children grow, particularly centered around traits such as gender and ethnicity, and behavior is heavily affected by peers for the first time.
  
  Adolescents undergo changes in behavior caused by puberty and the associated changes in hormone production. Production of testosterone increases sensation seeking and sensitivity to rewards in adolescents as well as aggression and risk-taking in adolescent boys. Production of estradiol causes similar risk-taking behavior among adolescent girls. The new hormones cause changes in emotional processing that allow for close friendships, stronger motivations and intentions, and adolescent sexuality.
  
  Adolescents undergo social changes on a large scale, developing a full self-concept and making autonomous decisions independently of adults. They typically become more aware of social norms and social cues than children, causing an increase in self-consciousness and adolescent egocentrism that guides behavior in social settings throughout adolescence.