Assignment of access rights to content, depending on age

[Kolobok]

I think it would be nice to add in HTML attribute xxx-level = [n], where n - an optional integer between 0 and 255 indicating the age (in months) is allowed to view the content inside the tag. Thus 16 years - this is n = 192, 18 - is n = 216, 21 - is n = 252, and the like. By default, n = 255. Pointing your browser's date of birth can prevent user to view the content of those sites where such an attribute will be used. And what is most comfortable - in detail on the tags.
What do you think about this?

P.S. Sorry for my English - the text translated by machine translation.

[zcorpan]

What's the use case?