I understand the appeal of a child-free wedding. After all, wedding ceremonies require the spectators to sit still and shut up, and wedding receptions usually have a lot of drunk people staying up late. Kids can't always handle either of those situations, and sometimes it's best to be better safe than sorry.
There isn't always an explicit cutoff for ages at a child-free wedding. Does a kid have to be 18 to attend a child-free wedding? Isn't a 16-year-old functionally identical to an 18-year-old in this setting, especially if you're in a country where you have to be 21 to drink? One bride put this theory to the test when she announced to her family that her intimate wedding of 30 people would be child-free. That would be all well and good, except that there is only one child in the family, and she's 17 years old. Feels pointed, no?