The thing you've requested might block a high amount of users. Even if they're over 13 there are lots of people who has learning disabilities and cannot solve such tasks. I'd suggest something more of a manual age check, or an age complaint protocol. in both ways the underage people will be addressed and taken action of. Also "printable consent" can be replicated easily, I'd suggest a voicemail of the parent. We do have a high amount of underage users but they're not showing any harm to the chat environment, their removal will cause mass losses in chat.