Nips went at 11 totally unchaperoned for 2 weeks. Originally he was going with a friend of his and his father, but his friend broke his leg a couple of weeks before camp. Btw, he flew this year as an adult, connecting flights and all..... I know that there are kids there that are even younger, but yeah, they are there with and older sibling or parent and are superskilled on the snow. I think the age is relative to how the kid handles himself alone. NO crying for your mommy in other words...
Ken Achenbach is very accessible, call him and talk to him and see how you feel about it. The key is when your kids have made friends so that they can travel in a pack, that way they look out for each other.