What is the design feature of a driver's license for individuals under 21 years of age?

The design feature of a driver's license for individuals under 21 years of age is the vertical format. This design element serves a clear purpose: it provides law enforcement and others with a quick visual indication of an individual's age. The vertical layout helps to distinguish between licenses issued to minors and those issued to adults, making it easier to enforce laws related to age-restricted activities, such as the consumption of alcoholic beverages.

In many jurisdictions, having a vertical orientation for underage driver's licenses reinforces the importance of age verification and can aid in preventing illegal activities associated with underage drinking. This differentiation is vital for both identification and public safety. Other materials or features, such as the layout being horizontal or incorporating specific colors, are not used to denote age status in the same way that the vertical format does.