Grim's comment under Boys and Girls, Men and Women prompted this extension. Most of the Wymans went to school in the South*. A college does not give one the full cultural experience, but we learned a few things, which gave us a basis for further learning from who we knew and what we read later. We learned that The South is many places and cultures (which you would never know from country music, where they are trying to sell records to as wide a range as possible, and so lump Jacksonville with Rockford, IL.) There is commonality, but not as advertised. Southern politeness and formality is recognised but not always understood. Grim commented on the OP about calling even female children ma'am. I wonder how far that extends geographically. Such usages, even when they have an undercurrent of humor, are never unserious. My son will give directions to his daughters "Ladies! It is time to get ready for bed!" When a coach or scout leader addresses the boys as gentlemen, there is likely something of importance to be said. They are being told to put on the role of gentlemen, at least for a moment. Calling boys "sir" is not mere mockery. It is a reminder.
The reverse happens when people speak about those of higher status as an Old Boys' Network, or at my hospital, the Old Girls' Network of nurses who were trained at our school. It is not a compliment, but something of an accusation that they are still functioning as children by favoring the comrades of their youth. Related: there is occasional discussion that it is unreasonable that black people can call each other niggah, or gay men say faggot, while it is a grave insult when outsiders do it. Sorry, that's how group language works everywhere, not just in America, not just in English. You can call your own group The Girls, and you can extend that privilege to your husband, though he'd better not call them that if you don't. Even your children might hesitate to say it in your hearing.
We used to refer to soldiers and sailors at war as "our boys." That was a common usage during both world wars. It was a common referent in the Civil War even amongst the men themselves. That tended to become less common between wars, and now I don't think it is common at all. Perhaps it persists in the south. I wonder if it fell out of favor with the coming of the volunteer army, or with more women joining the armed services? ("Our boys and girls" just doesn't work in a war context. You have to switch to "young men and young women.") In that usage I think it reflects our affection, and our recognition of their vulnerability as much as it acknowledges their youth.
Other subtleties of the usage would be welcome.
*For the record, two at William and Mary, two at Asbury, one at North Greenville, and one last who went to technical college in Houston. Plus I suspect some outsider knowledge is gained at Camp Lejeune.