Due to the body systems operating at optimal level and because typically individuals in this age bracket are in excellent physical condition, risky behavior and accidents are the leading causes of death in which stage of development?

Lifespan development is the study of how people change and grow from conception to death. It involves three developmental domains: physical, cognitive, and psychosocial. 

Lifespan development includes five stages:
Infancy: From birth to one year old
Toddlerhood: From one to five years old
Childhood: From three to 11 years old
Adolescence: From 12 to 18 years old
Adulthood: After adolescence