my 24 year old member was dating a 13 year old... I kinda wish such old members weren't dating kids or I wish instead of "break up" we could tell them to stop dating kids or something. Or maybe we could get both of them in the office somehow and make the older girl apologize so we'd tell the young girl to be more careful next time. Sorry if I'm thinking into this too much but yeah.
Since the player is not allowed to date underage idols, I can only assume this is a bug. I think underage idols should either not be able to be in relationship, only be able to have some sort of 'special friendship' with another idol (kinda like a relationship, but less blatant), or just be able to date other underage idols.