This question is inspired by several similar questions on this site.

The scenario: at one moment, all people above the age X disappear without a trace. How low this X can be that human civilization survives?

Obviously, 1 year old is too young, and 18 is arguably too old.

I set the following criteria of success:

 - Language is kept (which may change with time, it's Ok);
 - Tech level above stone age is maintained (at least in some communities);
 - Sufficient artifacts and knowledge from our current civilization
   survives, so, eventually, younger civilization can utilize it for a
   "reboot".

Children don't have to maintain world in order after the event. Any level of chaos and regression is acceptable if the rules above are satisfied.

P.S. Extra bit of information - there are apparently more than a few children under the age of 18 (likely thousands, if not tens of thousands) who are familiar with [Survivalism][1]. A proper "failure" scenario should mention how all of those children will be eliminated, or isolated for the rest of their lives.


  [1]: https://en.wikipedia.org/wiki/Survivalism