Not sure where you got that. If the purchaser is of legal age and has a valid ID, even if others that appear/are underage are around, the law doesn't prevent the sale - a business may decide to not sell, but it isn't a law that I've heard. I hold a permit and update it every two years, so it's something I encounter. Also, you can serve a minor in much of the US if they are with their parent or legal guardian. Most businesses chose to not do so directly, but generally won't cause a fuss if the parent orders and then serves the minor themself.