No I don't think so. Considering they said graduation was coming up he could be 17 or 18 depending on when he was born. If he was 18 while ending school he would be legally responsible. However he was coersed to sign.
Tbh that doesn't really matter, if you signed it you gotta return the money or youre dead. Law enforcement can't really help you nor protect you from ppl that will be after you 24/7, sure you can testify against them and show the police their face but without any proof of harassment it means nothing and even then they can still send other ppl to fuck u up
Okay so like he signed that as a minor right... so it's voidable...