Some rationale in Longmire's selection process:

World population 8 billion. (probably more, but it is just a number to start with)

Age 16-22 (roughly 10% of the population)
English Speaking  (about 5% as a first language and another 7% as a second language)

This leaves about 96 million

Now he has to parse this down to a manageable number.  Less than 100.  That is 1 in a million.  He is going to be very picky.

Weed out:
Royalty
Heirs to massive fortunes
People with too many ties to the rest of the world
Easy street lazy millennials who expect everything to come from Mom and Dad.  Over 18 and not in college or working very hard, a hopelessly jobless lazy bum who lives with their  parent(s)

The idea here is that he doesn't want divided loyalties.  Neither does he want people who would otherwise spend their lives on welfare.

I realize this presents a challenge for most of you to develop a character.  It sounds intimidating.  Well, Longmire is just that.  He has a John Wayne view of what makes a person worthy.  Here are some books or movies to think about.

True Grit
The Boxcar Children
(I'll add to this list later.  Food has arrived.)