Answer:
They should ask for some form of identification
Step-by-step explanation:
In clubs, or bars, whenever someone orders an alcoholic beverage (and they look rather young), the server should always ask for an ID or a drivers license.
This is because it illegal to serve alcohol to a person who is underage (a minor, in most countries is someone who is under 18).
Serving a minor alcohol can result in many fines and even jail time.
Many people who look young and/or short, are usually asked to provide their ID to prove they are over 18. For example, a man who looks like he's in his late 30's would not be required to produce an ID because it is clear that he is not a minor, however a man who is 19 may be asked to provide an ID so that it is assured that he is not a minor.