From what age should kids be introduced to adventure sports, for example; rappelling?

I was introduced to indoor rock climbing when I was 11 and at summer camp. So I reckon, thereabouts would a good age. By then, the child would have definitely mastered his/her motor skills, hand-eye coordination and have some form of athletic skills. I suppose you can try a younger age if your child is keen and if you find a place or instructor that is trustworthy, safe and has the equipment that are suited for a child's smaller frame (for example, the harness).