If you're an employer, there are lots of signals about a young person's suitability for the job you're offering. If you're looking for someone who can write, do they have a blog, or are they a prolific Wikipedia editor? For programmers, what are their TopCoder or GitHub scores? For salespeople, what have they sold before? If you want general hustle, do they have a track record of entrepreneurship, or at least holding a series of jobs?
These days, there are also a range of tests you can administer to prospective employees to see if they're right for the job. Some of them are pretty straightforward. Others, like Knack, seek to test for attributes that might seem unrelated, but have been shown by prior experience to be associated with good on-the-job performance.