You've seen him before.
At shul. At a host's home. Possibly overweight. Possibly unemployed or underemployed. Definitely single. His social graces are poor or inappropriate. He may make a comment that makes everyone at the table feel uncomfortable; or people pretend not to notice. The host is apprehensive about inviting him back. The host isn't concerned for his children's safety, but he does worry that the guest will do or say something inappropriate--perhaps something the child will remember. He can't quite put a finger on it, but he doesn't want the guy to return. As a result, the guest's hachnachas orchim (overnight/meal hosting) choices are increasingly slim--almost as slim as his dating prospects.
I don't know what the answer is. I wish there were some way to reach out to these men. "Meeting for weird guys: Sunday, 3pm" probably isn't something that one might see in next week's Likutei Peshatim. I wish his hosts--friends who know him well--would reach out to him and try to tell him, in a nice way, "It would be helpful for you--in career, in dating, in this community--if you would ________." And that could be a number of possibilities. "Stop talking to young women." (I'll get to that in a minute.) "Use a more direct tone rather than a sing-song voice that might sound gay." "Dress nicer for shabbos, and find better-fitting clothes." "Don't stand so close to people." I've seen guys in the communities in which I spend time, and my heart goes out to them, for the most part, because I believe they just don't get it. They don't realize how "off" they are, or how strange they appear to others. My sense is that most people don't like "strange" because they associate "strange" with "surprise," and people don't like surprises or situations they cannot control. And the latter is something they fear. So these guys remain outside the mainstream.
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I need to do some polling on this. Here is what I think: young women, and especially beautiful young women who are noticed often, are easily creeped out by men much older than they are who try to chat with them. Regardless of how they feel, here is also what I think: it's not cute, it's not appropriate, and these weird guys need to shut up. Here's a clue: you're pushing 60, and she's 24. "Gut shabbos" is enough. She doesn't want to tell you how she is, as much as you'd like to hear it. Way too many weird guys get an ego boost by playing "20 Questions" with young women. "Oooh, she talked to me," he'll say to himself. Well, she wasn't happy about it. It puts the shul in a difficult position as well. Here's a guy who doesn't have other shul options. Or if he does, the shul doesn't want to make another shul angry by dumping this difficult member on another shul. Meanwhile, the guy is making young women uncomfortable in shul, which is supposed to be a safe area.
So it can't be the rabbi's problem. It should be the Membership Committee's problem, in conjunction with friends of the guy or friends of the women he likes. They need to lay down the law, or layeth the smacketh down, if it comes to that: stay away from her.