the thing is it's not just about when the conversation is a matter of urgency or real life risk relevant that's the issue - it is whether you've cultivated a conversation over years and years - whether you've cultivated a climate of open discussion - whether you've grown the conversation.
there's no shelter till age x and then expect to be able to have conversations about serious stuff that have an effect. if you are behind what they're actually learning you will be behind their credibility itms - as in by leaving it so late or not engaging in a progressive conversation about reality, sex, risk, real life etc etc etc from early on you cease to be the person/source/resource that they'd come to.
if you imagine consulting a newspaper or website as a credible source of information and guidance how many times would it need to be out of date or mollycoddling you or not telling the truth or engaging with where you're at before you'd write it off as unreliable and/or a bit thick or deliberately misleading?
i don't see how you can say this is the age for conversation x - surely your children tell you when the time is if you don't preempt that and lead the way? it's not a one off later on talk about 'internet safety' it's a constant, open, ongoing conversation about life and how to be ok and how to be happy and how to cope with complexity and risk and boundaries etc etc.
i don't get how you can see it as a discrete answer to a discrete issue at a discrete point in time.