This should help people who have to monetize lots of videos on YouTube at once.
Click “My Channel” on YouTube.
Click on the “Video Manager” at the top.
Click on box top left.
Click “Select all your videos.”
Click “Monetize with ads.”
Click “Submit.” Now all you have to do is wait, this may take some time depending on how many videos you have.
I hope this helps with monetizing all your videos at once.
FOR MORE INFORMATION ON VIDEO MONETIZATION CRITERIA FROM YOUTUBE CLICK ON THIS LINK HERE.