Although they may be the same size as their parents, young adults are still developing physically, emotionally, socially and sexually. Each individual follows his or her own trajectory to full maturity, as genetics, experience and environment all affect development. When dealing with a young adult, parents should continue to share values and provide guidance, but respect their child’s independence, privacy and need to make their own decisions.
Physically, 18- to 20-year-olds usually look mature. Many have reached their full adult height and have fully-developed physical and sexual characteristics. Women’s breasts have usually reached their adult size, while men have full beards. Both display adult muscle mass. Some males in the later teens are still growing, however, and may continue to add inches or pounds until they are 21, according to the State Adolescent Health Resource Center. Young adults are typically healthy, although the Palo Alto Medical Foundation notes some may be dealing with chronic diseases or medical problems such as diabetes, asthma, obesity, sleep disorders, sexually transmitted infections or hearing loss from media players.
Cognition -- the ability to think, reason and make decisions -- is one area where young adults are still developing. Brain development does not peak until the twenties, so an 18-year-old may still display “teen brain” and be more impulsive than a 21-year-old. Young adults can comprehend abstract concepts, having a better grasp of consequences and personal limitations than adolescents. Although brain structure is the same for both sexes, connectivity in the brain differs, according to a study from the Perlman School of Medicine at the University of Pennsylvania; women can often think more intuitively, while men may be better at following directions. The researchers note that these differences typically become more pronounced in young adulthood.
Emotionally, young adults are beginning to move into adult relationships with their parents and other adults. Although they still develop strong friendships, the peer group has less influence on their decisions than when they were in their early to middle teens. SAHRC notes that part of their emotional development is the ability to develop romantic and sexual relationships. Gender identity and sexual orientation may be more fluid at this time of life, as young adults experiment. Young adulthood is often the time of the first serious romance, sexual experimentation or true intimacy and marriage. At this life stage, the individual is also developing and strengthening personal values, which may be similar to or different from those of their parents.
Young adults often experiment with different roles, according to the Child Development Institute. Still in the process of determining “Who am I?” the young adult may explore different educational options, try working at different jobs or move in and out of social groups. Young adults are often idealistic and may become involved in social issues such as inequality or the environment. They may also volunteer or work in community development activities. At this stage of life, the Young Adult Development Project notes the young adult begins to think about the future and people's roles in life from a more global and holistic perspective than an individual and personal one.