Yeh, YouTube doesn't have anything super mature because of the TOS. Don't tell your parents, he'll hate you for doing that lol. What browser are you using? Just block YouTube, I'm pretty sure you can also set a password for it so you can be able to watch videos when you want to.
Also you said he's 14 so you should be expecting stuff like this.
meri jaan tu abi 14 b nahi hai aur advice dera hai... shabash shabash