I'm a legal consumer at 22 now, but I have been served onboard DL since I was 18 without any questions. However, when I was 19 and traveling for business and dressed to fit the part, I stepped into a bar/cafe similar to Sam Adams at Hartsfield and this rather large bartender leaned over the counter and stared and said, "I need to see your ID son". Needless to say I could have crawled under the bar stool!