Officially, 21 is the minimum age for Delta flights:
For example, American Airlines confirms they adhere to U.S. law,
telling Traveler: “Since we’re based in the US, we go by the
21-year-old drinking age.” Delta, United, Alaska Airlines, Virgin
America, Southwest, JetBlue, Spirit, and Allegiant are the same,
drawing a line at 21 and up for serving passengers alcohol onboard.
As a practical matter, they are unlikely to be too concerned about your age, and it’s fairly uncommon to be asked for ID. If you’re asked if you’re over 21, I’d tell the truth.
Credit:stackoverflow.com‘