@ariarhythmic
This maturity signal I'm talking about is a way to mark that someone is capable of fully understanding what it means to enter sexual relations (be they faux or real) with someone else. Because no matter how much you preach human beings' agency, young people who think they are ready keep getting abused, blackmailed, and otherwise scarred for life even by people who didn't mean them harm.
It's protecting people who don't know better from making decisions that they are going to regret for the rest of their lives, at the expense of not letting them go places where they aren't welcome anyway. This same idea is why we have driver's licenses, extensive permitting around working with hazardous substances, and certifications for dangerous jobs.
Though while those certifications are used to prevent harm both to the person practicing and the people around, this one only protects the individuals who want to make sure they are on even ground.