Thanks, Willow and Ange,
I loved working with high school age kids MOST of the time. But of course, their judgment is not fully formed and they make mistakes, as do we adults. I don't know what "border" you mean, Willow. Canada? I see that all surrounding states have a 21 minimum. (When I was growing up there, NY was 18, and many young men and women from MA and elsewhere lost their lives driving drunk back from there.)
True: I would not be there. I believe that does make "trust" the key factor, and since I don't know the young man who inquired or his 3 (only?) friends, I worry. Also, having daughter, I remember all the "small parties" that got out of hand as additional guests showed up—not at my house, by the way.
The local law is important. Here is CA, the host is criminally liable for allowing underage drinking. Fines are steep. And there are stairs with open railings, second floor deck, etc. Lots of things that could go wrong.
Thanks for your input! Leaning toward "No."
JB