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 YouTube has 18+ content? 
 Yessir.

https://support.google.com/youtube/answer/2802167?hl=en

Things such as sexual intercourse, surgeries, war footage, violent rhetoric. 
Unfortunately they include way more than that in the grouping but those are some more extreme examples.

That doesn’t touch on the other at least two categories.

“restricted mode”
Or 
“Kids mode” 
which are opt-in.