Wouldn't this mean we don't know what age these 10% are in?

i dont know what point you are trying to make.

there are laws against underage drinking and buying alcohol. some kids still get access to alcohol. the law is mostly successful, with an acceptable amount of failure rate.

same concept.

Gating is not just for porn, they are talking about using for social media and various other things. You can imagine that many things end up age gated if this becomes legislation, as a preventative measure.

Then your 10% becomes problematic because you are either restricting or granting access based on invalid information. So in your world here we then need ways for people who were incorrectly gated to reach out and be corrected somehow.

You're mixing up false positives and false negatives. Nobody is going to be incorrectly blocked under this system unless they lost their ID, and the fix there is getting a new ID.

Some kids skipping the block sometimes isn't catastrophic, especially because there won't be all this peer pressure to join adult social media when 90% or more are blocked.

You know this? My guess is that companies will be held responsible for anyone accessing there content that is not supposed to. In that light they will feel the need to block any unknowns that come through rather than potentially face issues if someone who is technically banned from accessing gets in.

I'm not sure how you confidently can say that every company is going to allow the people we can't verify have access?

No, it means Instagram doesn't know.