Physical development

During middle adolescence, from about age 14 to 18, physical growth is usually completed for both genders. Most girls stop growing in height by age 16 and boys by age 18. In most cases, teens grow taller before their bodies fill out. Weight gain during puberty often accounts for much of an adult’s total body weight. In middle adolescence, muscular mass and strength continue to increase in boys, while lean body mass decreases in girls as body fat shifts for storage in the breast, abdomen, and upper back and hip areas.

Bone maturation, which is controlled by hormones, usually occurs after elongation (bone growth). This disparity can increase the risk of bone fractures, especially when teens engage in high-contact sports. Sports safety should be practiced to help prevent such injuries. A middle teen boy’s facial and body hair also begins to increase noticeably during this time.

During middle adolescence, the heart doubles in size and so does lung capacity. Blood pressure, volume and total blood cell count also rises, especially in boys. Teens now generally require at least nine to 10 hours of sleep a night in order to maintain optimal daytime alertness – more sleep than at any other time in life. Lack of sleep can have a negative effect on a teen’s mood, school performance and cognitive function. Studies also show that young people between 16 and 29 years of age may be more likely to be involved in automobile accidents due to falling asleep behind the wheel.

By middle adolescence, most teens have undergone puberty. Girls who have not begun menstruating usually do so by age 15 or 16. Onset of menstruation is usually determined by genetics in addition to factors including weight, chronic illnesses (e.g., diabetes) and exercise regimen. Many girls have their first gynecological exam during middle adolescence. However, health experts generally recommend that adolescent females who are sexually active, regardless of age, be examined by a gynecologist (physician who specializes in female reproductive health). Both the American Academy of Pediatrics (AAP) and American College of Obstetricians and Gynecologists (ACOG) recommend that adolescent girls see their physician for preventive healthcare visits to discuss their reproductive health, and help establish an environment where they can feel comfortable discussing health concerns. Between ages 14 to 18, boys’ sexual organs develop in size and those who have not done so already begin to experience nocturnal emissions. Voice changes may also continue in boys during middle adolescence.

Cognitive development

During middle adolescence, most teens begin high school and intellectual abilities are typically enhanced. This prompts many to question and analyze life more extensively. They often develop a personal code of ethics, which corresponds with their own beliefs and behaviors.

This new flexibility of thought has a major impact on an adolescent’s self-concept and relationships. Many begin to philosophize about the meaning of life as well as their purpose in it. Most adolescents between age 14 and 18 also start to think about the future and make plans regarding goals such as college and career paths.

Middle adolescence is a time of great variation in cognitive development among individuals. In addition, the difference between thought patterns at age 14 and age 18 is vast in both girls and boys.

Psychosocial development

During middle adolescence, a teen’s group of friends may exert less influence over them than in early adolescence. This stage is commonly characterized by plenty of experimentation. For instance, a teen may change fashion styles, groups of friends and personal interests from month to month until they discover what suits them best.

Because physical growth typically slows down at this time, teens may become more comfortable with their bodies. However, many teens also begin to experience strong emotions and rapid mood swings. Most middle adolescents continue to distance themselves emotionally from their parents in their quest for autonomy. They often channel all their emotional and sexual energy into personal relationships.

Middle adolescence usually involves a growing interest in dating. This can become an issue of conflict between teens and parents as adolescents strive for personal identity and autonomy. The past experience of the parents often influences how they cope and are able to negotiate this formative phase with their teens. Parents and other caring adults are encouraged to promote open communication while helping children make responsible decisions.

Sexual activity often varies in teenagers aged 14 to 18. The rate at which teens develop physically and sexually (puberty) in addition to societal pressures can influence sexual activity. Masturbation is very common in middle adolescence. Some middle teens engage in sexual intercourse, while others experiment with petting, kissing and mutual masturbation. Teenagers may be curious about heterosexuality, bisexuality and homosexuality. Sexual orientation is not necessarily decided during middle adolescence.  

Physical attractiveness and popularity remain important issues, both for personal self-esteem and a teen’s comfort in the ability to establish relationships. Middle teens typically spend a lot of time thinking about themselves and obsessing about physical appearance. They also tend to assume that everyone else is scrutinizing them. Self-centeredness is entirely normal at this stage of development.

A downside to this heightened self-awareness is that adolescents with physical conditions that are considered unattractive, such as acne and obesity, are at increased risk of being teased and experiencing low self-esteem. Teasing and low self-esteem can result in teenagers having difficulty in forming healthy, satisfying relationships.