I wouldn’t go so far as to fill a glass at dinner, unless you know their experience and tolerance. And judgment. What I mentioned was just a toast and done. Dilute it with something, if you want. As far as mocktails, most kids can’t tell the difference. But I do think a light attitude (“Hey, at OP’s house, she served me 6 “drinks” and I didn’t get a buzz!”) could send the wrong message.
We’ve had problems in our area with parents “hosting” big parties with alcohol, lots of kids, then disappearing. Big problems, legal action. But I wouldn’t be doing that and nor is OPtalking about that.
The problem the last time some states lowered the age to 18 was a serious increase in alcohol related accidents. There is no way to simply aay, wth, they’re over 18. (But I have isue with compusory military service at 18, too.)