In most cases you will get guys who have tried another sport and failed. So I'd guess roughly 22 years old.
If that background was NFL, They won't know how to tackle or attack depending on the position they play.
Womens will be easier as most come from Rugby or something but putting them with players who have years of experience is hard.
But it is good publicity especially if it grows annually. You never know someone there for the double header my see it and invest in the local game. Another bonus
The age and experience of the athletes that attend will depend on the NRL's criteria to attend. The majority will be former collage athletes that missed out on going pro, but there's nothing stopping the NRL casting the net wider and inviting people from other walks of life if they choose. There're plenty of quality former high school athletes and collage dropouts kicking around in America who could still make it in sport if they were given an opportunity.
With the possible exception of a handful that might have some experience playing high school or collage rugby, and that would be a tiny percentage, it's unlikely that any of these people will have much of any practical experience that's applicable to playing RL. But that doesn't really matter, quality athletes can learn that stuff relatively quickly if they're dedicated and have good coaching. Mason Cox was a college basketball player and high school soccer player with no experience playing a full contact sport at a high level before he was picked up by the AFL.
Lots of people outside of America don't understand just how much athletic talent is going to waste over there. There's a massive oversupply of top quality athletes, only about 1% of which will ever make it pro in the major leagues. A huge portion of those leftovers have the means and ability to make it in another sport, the problem is that nobody has been able to come up with a reliable method of connecting those people with opportunities in other sports and leagues overseas yet.
That is what I reckon.
Still they go home and strengthen the local comp with that experience is a positive
That almost certainly wont happen.
The people who enter the NRL's combine and win a contract will be doing it in pursuit of a career, not for any love of the game. They'll move on to the next best opportunity to make a living if this one dries up.