I've never advertised an age restriction, however, I do have one. When I get the idea he's younger, I ask him personal questions to make sure he wouldn't directly know my son. So far it has worked, however my son has now ventured out beyond my knowledge so it's becoming more of an issue.
In Saskatchewan is a big example. He spent many years there, and his friends list is Vast. My client list will get older as he ages ~sigh~ Right now he's 24, but has friends much older. *dont add up his age with my advertised age: I had him in high school

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How uncomfortable would it be if you 'saw' one of your adult child's friends, and they were invited over for a bbq ?
My last trip to Saskatoon, I saw a client who spent 2 months in my home with 4 other SK boys who wanted to work in the oil patch. He looked different when at the door, but his eyes where the same. We both recognized each other but nothing was said. I hummed and hawed about telling my son who I saw. ~how awkward~ Over lunch this week, I brought up a question to him, "what if I saw one of your friends" He laughed, (you know that uncomfortable laugh we all have). He replied: whatever. A little bit later he has finished processing and asks; have you seen one of my friends ? I replied with Yes, one of the boys that stayed at our house back in 2007. When I told him, I told him so if this kid says anything to my son when he was drunk or pissed off for unrelated reasons, that my son was prepared. Which I explained to him ! My son's reply was "I'd pop him in the mouth"
Age restrictions are there for a reason, and the lady shouldn't have to explain why !!