Very PUBLIC places, DY. I doubt a truly frum boy or girl would be likely to get into trouble under those circumstances. And if they WERE, then it could and would happen anywhere, unless they were kept in isolation from each other. We have to start trusting our young adults to behave with the proper derech in which we have raised them. Not talking to each other until they are redt a shidduch, is NOT making them frummer or better Jews (though I suppose you would disagree, and that’s fine, because you have your opinion and I have mine). I believe that over the last couple of decades this has in fact hampered many young people in their ability to grow up socially normally.
I understand that this is Yeshivishe way, and I can respect that philosophy, while absolutely disagreeing with its efficacy. We DO have a shidduch crisis today, and it is not IMO because of an age gap. It is because by the time people wake up and realize that they have grown much older while waiting for the right shidduch to finally be redt to them, they have missed the opportunity to meet people, possibly on their own, because it is “just not done that way.”