Minimum age to ride a stallion in endurance

[guest@endurance.net]

Sarah patchworkfarmshorsestuff@hotmail.com
What is the minimum age that a rider can ride a well behaved stallion in
endurance?  I really wanted to ride my own mare in endurance this year,
but i have a young boy(12) that wants to ride my stud in endurance.  His
dad raises and races standardbreds and this young boy jogs them horse his
dad, and he is just great with my stallion.  He handles him really well.
Would he be allowed to ride my stud?  thanks ya'all!