Final answer:
In the United States, you need to be at least twenty-one years old to serve alcohol.
Step-by-step explanation:
The legal age to serve alcohol varies by state in the United States. However, the National Minimum Drinking Age Act of 1984 requires all states to set the minimum age for serving alcohol to twenty-one or risk losing a significant amount of federal highway funds. This means that in all states, you need to be at least twenty-one years old to serve alcohol.