This is a fair point. Primarily the reason that children can dominate a website is that they have so much more time to participate (and probably are more likely to contribute in a low-effort way), so putting the mark at 16 or 17 would still significantly reduce the issue. I think having places that are certified <12 would be great for kids and could be over-moderated without great consequence. A spectrum of age gates would make a very cool internet, and I'd extend that as far up as ages go (35-55? Centenarians only? Why not?).