^What my buddy B Jangles said;
The legal complexity of the age verification goes far beyond that, guys.
technically, the owner of the content cannot be held responsible for it if he warns about it or ask for age (even though, as previously established, everybody lies), just like the ESRB filters.
Basically you can understand the age verification as:
"Im gonna upload some porn, and I dont want a lawsuit on my ass so Im gonna ask for age and if the user lies about it to watch the content, then its his/her responsibility, period".
Damn Im truly an awesome lawyer, I should go to Harvard...again!!