It’s not modern. It actually echoes a time of poverty and how down to family we are.

Even in a house with more than one bathroom, the notion that one is for boys and the other for girls is very, very rare. Doesn’t make sense.

Old restaurants and similar places were usually family owned and even run from a part of the house. The money and/or space to build two bathrooms just didn’t exist so sharing was the only available option. And be civil about it. Or get kicked in the ass for being a slob or rude.