Everyone over 21.

For some reason beyond your comprehension, it's an unspoken rule on Obasaan that everyone should be wearing diapers while not at home, if not also at home. Some say it's because of the trip to Obasaan having some affect on people's muscles or their nervous system, some say it's the minerals present in the soil of Obasaan, and some say it's just the culture that spawned from the fact that moon colonies are built on the backs of the craziest and most reclusive people in our society.

In any case, everyone over 21 on this moon is expected to wear diapers, at least while not at home where presumably, you can get up to use the bathroom as often as you need and it's never very far. It sounds like some people will choose to wear diapers before turning 21 or while at home, as well.

You hope there's a bit of a grace period for new arrivals as you see a flight attendant with a noticeable bulk under her skirt, as there weren't any good quality ones back home for a reasonable price.