I have seen lots of horses over the years that would take care of children
and when mounted by a rider who knew there stuff, the horse would wake up
and be a fun ride. I think the answer is training and not too young. Look
for someones horse that is a fairly good rider/trainer. Look for quiet
ground manners.
As a mother of two sons who rode in their youth, but no longer ride, and a
4-H and Pony Club leader, I really suggest you never overmount boys. Girls
seem to handle that much better, and have a better understanding of
animals. Of course, I am speaking in generalities. A lease is an
excellent idea.
Have fun shopping,
Bonnie Short