I'd really like to steer away from age entirely. This requires that we have universal rules about what content is appropriate for what age, which I don't think

I'd really like to steer away from age entirely. This requires that we have universal rules about what content is appropriate for what age, which I don't think is necessary. For kids, why not let parents decide. And why not also use this infrastructure for adults. NSFW buttons are so common that it's clearly something that adults want too.