In the US, many mobile home communities require tenants be over the age of 55.

I’ve seen weird rules too, like 50% of the household must be over 55. So like if your spouse is younger but you are older than that is okay. This pretty effectively does a good job of restricting children just based on math and family dynamic without explicitly stating “no kids”.

One of my parents used to live in such a community. It was quiet as hell at night.

So restrictions like that are clearly legal and not considered ageism. (I might have considered living in that same community if I were old enough.) But apparently restricting children would be illegal?