I don't know how this one got $7,000 but I do know that some teenagers have jobs and it isn't very hard to save money when your needs are taken care of due to living with your parents.
I'm pretty sure that can be cleared with a bankruptcy. Considering a 19 year old isn't likely to have any non-exempt assets, they can go bankrupt with basically no penalty other than having a bankrupcy on their record for the next 7 years.
When you short a stock, you borrow a stock, then sell it, then you buy it back at a (ideally) lower price. Then, you have to give back the stock plus interest. This person can’t sell the stock because they have to give it back. It wasn’t theirs to begin with. They were just borrowing it.