I don't think the Cleanser poster is exhaustive. It leaves out things like health information (e.g. immunity status) which must surely be taken into consideration.
Also, we don't actually know that Emil didn't have to get parental permission! It's not the sort of thing he would mention.
The 'when-are-you-an-adult' thing has varied wildly across cultures. I believe that in its later stages the Roman Empire had a pretty wild disparity between when a boy stopped being a child (and could fight in the army, etc) which happened at 14-18 or so (depending on the time period) and when he became a man considered capable of making his own big decisions. (Around 25, ha -- before that he would have to go through a guardian.) That's a law Onni would have appreciated, I am sure.
Women didn't have this, of course.