A recent update to the Twitter-owned Vine app for iPhone bears at 17+ age rating. The update, version 1.5, doesn't mention the change in its release notes, but users downloading the app will see a pop-up message noting that Vine may contain age-restricted material.
This is no doubt a response to a brief pornographic video somehow being presented as a Vine editor's choice last month, shocking many users.
Vine lets you create and share 6-second video clips. In my experience they're kind of jarring, but in the right hands, perhaps someone can create something beautiful.