Did we ever learn how old they all are? Everyone on the show seems to think they're "kids" and refer to them as such. I'm only about halfway through re-watching Season 1, and I've learned Kid is at least 18 (His brother Jed tells a story of something that happened when Kid was 8, and says he hasn't seen him in 10 years).
Historically, pony express riders were very young, in their early to mid teens. The ad called for boys under the age of 18. Cody, for example, who really did ride as an express rider was only 14. But, let's face it no one wants to watch 14 year old boys riding around America...we want sexy twenty something men fighting for justice! So, the age of the "boys" is never given.
Hope that helped answer your question a little bit!
Except Kid's then, whose was hinted at in the Jed episode. It just kind of strikes me odd how everyone dealing with these guys instantly assumes they're children when they all look in their 20s. Suspension of disbelief, I guess.
"Historically, pony express riders were very young, in their early to mid teens.The ad called for boys under the age of 18."
Actually I think you are talking about the ad which said that orphans were preferred (so if they were killed, they wouldn't have families to sue the company, I suppose).
But that ad was not quoted or mentioned until many decades after the pony express rode. It was not actually used in 1860.