I remember when the drinking age was 18 and the voting age was 21. The country was a lot better off then.
Really, under what possible circumstances would anyone offer alcohol to teenage guests? Kiddush wine? maybe. L’chaim? I don’t think so. Wine with the meal? Only in France.
Whether or not a violation of law occurs apparently depends on the individual State’s laws. (See post by yitayningwut above)