I think you have a very good chance of them hiring you especially if you have a profitable track record, age doesn't matter. Why not send them an email?
I'm fairly certain they don't pay any salary, you just get a split of profits usually 50%-90% depending on your progress. Otherwise you can put money into an account to cover your risk and back yourself for 100%, you'd just pay a desk fee.
They are a services company they tend to provide traders with what they need in return for a desk fee and a commission of a few cents on each trade you do. It's by far the cheapest way to trade if you do so actively.