> Why on earth should 18 year olds be entering financial transactions over hundreds of thousands of dollars, where they, but not their counterparty, get to shoulder all the risk?

I'm a firm believer in maturing before entering a transaction like that. Maybe even "taking off a year" or working full-time for a bit to understand how "the real world" may work from what you understood it as at home (hint: it's much easier for some than others).