Age prediction
Estimating how old a user probably is from their behaviour, rather than trusting what they typed in a box.
Age prediction is a service quietly guessing your age from signals it already has: how you write, what you ask for, when you are online, what you interact with. It exists because the honest alternative does not work. Asking people to state their age is trivially easy to lie about, and demanding an identity document keeps out plenty of legitimate adults who do not want to hand one over.
The design question is what to do when the guess is uncertain, and the safer answer is to assume the user is younger and apply the stricter rules. That protects minors at the cost of occasionally restricting adults, who then need a way to prove otherwise. AI chatbots have started shipping this, which means the system is forming an opinion about you and acting on it without ever asking.