depends what you're looking for out of the experience and what your goals are. i liked coaching 7-8 year olds because none of them have poor fundamentals to the point that it's difficult to get them back (or to the point that they're stubborn because they're performing better than the others and don't want to change what's giving them that performance)...so you can make sure they start out right.
This crossed my mind as I filtered exactly what I wanted to do. I was thinking like Kam, 9,10,11. But that sounds along the lines of what I was hoping to accomplish. Do 7,8 year olds wanna play defense? Win? I can't remember my mindset at 8.