There's a site that you can use by adding nsfw in the front of the YouTube domain (so you get nsfwyoutube.com), but last time I tried it didn't worked. Not sure if it was a temporary issue or if YT is blocking them.
Youtube has stepped up their game wrt to age restricted videos. You are now forced to watch them on youtube.
Previously could get around it using the /embed/ url or third party sites like youtuberepeater. Seems like these methods have been closed.
> It's using technology to identify age-restrictive content so that when viewers discover age-restricted videos embedded on most third-party websites, they will now be required to log in to watch those videos in order to verify their age.
If you have VLC installed you can copy the address and then past it into VLC then select the play option. It works most of the time, and worked with the first video I tried.
You can also enqueue them, if you want to play more back to back. I normally use it in conjunction with the RSS feed of channels.