Oh. I forgot one other thing . How many people drank underage? yet tell tell youths not to drink.
That has nothing to do with ethics - that is learning from your mistakes.
Denying children good advice simply because you made the same mistakes would immoral. If anything
your experience lends credibility.
Even so, explaining how it feels to pay homage to the porcelain god and what a hang over feels like never quite has the same effect as a parent seeing a teen in the midst of such unpleasantness and saying, "so, learn anything new today?"