How to give a website a content rating beyond just "adult"

Question

Is there any generally accepted way to give a page a content rating beyond just "adult", such as PG-13 or equivalent?

All I can find is the <meta name="rating" content="adult"> and <meta name="rating" content="RTA-5042-1996-1400-1577-RTA"> tags, but they seem limited to one rating only.

From Google's SafeSearch documentation:

One of the strongest signals our systems use to identify pages with explicit content is when publishers mark such pages (or indicate in headers) the following meta tag:

<meta name="rating" content="adult">

Note: Google also recognizes <meta name="rating" content="RTA-5042-1996-1400-1577-RTA"> as an equivalent way to identify pages with explicit content. Either tag is fine; it's not required to add both tags.

No mention of other ratings. Likewise, the WHATWG page on Meta Extensions only mentions adult content:

The Restricted to Adults label (RTA) provides a way for adult oriented websites to indicate that their content is off limits to children. RTA was introduced in 2006 and is currently used by a large number of adult web content providers. RTA is recognized by all major parental control filters.

What do I use if my page is not exactly adult material, but might still not be appropriate for young children?

Answer 1

To my knowledge, there is no generally accepted way to give a web page a machine-readable content rating beyond the "restricted to adults" or "RTA" tag that you mentioned. Some questionable reference materials seem to list additional values for the tag, but I don't believe there is any standard for those values, which means that they have no real utility.

I think it's worth noting that technically, Schema.org looks to be expressive enough to communicate age restrictions. One might use a WebPage object with an audience property, setting it to a PeopleAudience object with a suggestedMinAge or requiredMinAge property. However, this is not a generally accepted way of doing things, so third parties would not be able to draw meaningful inferences about your page based on such tagging. It would add complexity to your meta tags for no benefit.

Also worth noting is that there's a short yet pertinent discussion of age limit meta tags at this w3c github issue. It mentions two prior attempts at age rating meta tag standards, PICS and POWDER, which failed to maintain traction.

What do I use if my page is not exactly adult material, but might still not be appropriate for young children?

In my opinion: nothing. You could consider adding a verbal warning to your page that it is unsuitable for small children, but a small child may not be able to read, understand, or internalize the warning. Since there's no agreed-upon meta tag, there's nothing to consider in terms of tagging. With all that in mind, I would say it's pretty firmly "not your problem" - it's the problem of the parent who is letting their young child browse the internet unsupervised.