This is all voluntary.
We all know that schools and parents are always trying to teach us to conform to a textbook norm. Their intent might be "For the Best". But, when it comes to those 18 and up websites, why not make an DNS record to indicate the age-appropriate content(age-ac).
My Idea that would help parents and schools to "filter or Block" age restricted content:
DNS RECORD: In TXT
Syntax: age-ac="{fam/pg/13/16/18/xxx}"
I would recommend an TTL of 24H/48H as this would probably not change and should reduce query response time.
This in my mind would then allow your ISP or your device to "Filter or Block" unwanted content. This should be great for when you are at work and you miss click...
And as for Kids at school, The world is your oyster! Pref. use the Internet!! and never trust a word a teacher says.Ever.
My grade 6 teacher taught us ¼ - 4 = 3 ¾ .
Sigh...
This is open information. Public domain and you may do with this as you may. But just keep the SYNTAX the same! We don't want a gray area... 
