It means they want her to hang from a rope/belt and die. Yes, it is a threat, it seems to be like saying “I hope you die.”

I’m probably the second youngest, I just turned 18 earlier this year.

This user, I believe is around 14.

Their friends mentioned are all 14 and one 13, so I’d also assume if these are close friends, that OP is 13 or 14 as well.

Edit: A post from 2 months ago states they’re 13, and that would be sometime in January before the 13th most likely. OP’s bio says Jan 25th, so they probably turned 14 and are in 8th grade.