In some Youtube Videos, you can't watch it because of restriction. This may happen because of the content of the video is not suitable for every age to watch. Here is some easy trick to bypass it.
If you want to stay on the official YouTube site, you can just remove the 'watch?' in the URL and replace the '=' sign with a '/'. For example:
This bypasses the restriction and lets you go straight to watching the video without the age confirmation.
If you don't mind being redirected to a different site, you can instead add "nsfw" in front of YouTube in the URL.
This takes you to a site dedicated, as the name suggests, to letting you watch YouTube's NSFW side to your heart's content.
Now you can watch the NSFW video without any permission.