At what age are individuals required by California law to wear a properly fitted and fastened bicycle helmet while riding?

In California, individuals under the age of 18 are required by law to wear a properly fitted and fastened bicycle helmet while riding. The correct choice, therefore, is 18 years of age. This regulation is enacted to protect young riders from potential head injuries in the event of falls or accidents, as helmets play a crucial role in absorbing impact and reducing the severity of injuries.

This law emphasizes the importance of safety measures for minors as they may not always have the same awareness of road hazards or riding safety that older individuals do. Consequently, while the options of 16, 21, or 14 may seem like possible ages, they do not align with the specific legal requirement established to promote safety among younger cyclists in California.