1. 3 to 33 yrs
Fatality related to motor vehicle traffic is the number one cause of accidental death and motor vehicle collisions are the leading cause of death for people ages of 3 to 33 yrs.
From the web:
Motor-related injuries are one of the leading causes of death among children, adolescents and adults between the ages of 3 and 33 in the United States.
Source: [link]