What Age Is It Okay For Kids To Go Trick Or Treating Without Their Parents?

My children want to go trick or treating this year with their friends. Which leads me to ask other parents at what age is it appropriate for children to go with a group of friends without adult supervision? If it was up to me it would be 22, so I realize I need some rational advice here.

So at what age did or will you allow your children to venture out and trick or treat without you?