Come on a minute -http://www.fellrunner.org.uk/2009racesjunior.htm - 62 races here all juniors.
http://www.bofra.co.uk/fixtures.php - 31 more races here.
If you also add in to that the U16s can do Senior Races that are up to 4 miles and if you are U18 you can do senior races that are up to 6 miles.
WPette has done a few A category senior races and she is still only 15.
So I think there are plenty of races here for the juniors - WHO SHOULD NOT BE FOCUSSING SOLELY ON THE FELLS!!!
If you do - then that would be a more likely reason to drop out - get some road, XC and track in as well!
Also, please bear this in mind. I was involved in the FRA at Darwen. With the short AS Senior race, we could manage with around 6 - 8 marshalls.
As soon as we add in juniors, the number of marshalling points doubles.
Imagine trying to manage the logistics of a 800 runner event such as the 3 Peaks, and trying to put on a series of junior races.
AS outlined above, there are enough junior races.
Juniors would learn more by going camping at Borrowdale / PPP etc, watching the race, talking to the athletes before and after and seeing how they cope with the race.