When Should Kids Stop Trick or Treating?

Hello everyone! Well, Halloween has come and gone. I am thankful it is over as soon we will get to focus on Christmas. We love Christmas around here! I have a pet peeve, though. And from talking to my friends, it is quite common. We recently moved to Katy, Texas. We also moved into a neighborhood. Before, living out in the "country" we had no trick-or-treaters. So...I was excited to be able to give out candy to princesses and goblins. And my kids had their own neighborhood to go out in. But, we had a lot of old kids trick-or-treating! I mean old boys (I think all the old kids were boys) ranging in age from 15-17 or 18!!! And all but one of these didn't even bother with a costume or makeup or anything! I silently debated telling them they wouldn't get candy. But, I did give candy to all. I am a little mad at myself now for handing them candy. Where are these kids' moms? What type of parent sends or allows their kids out to do that? I would never do that!! I had to ask two of the groups of these boys to please not cuss around little kids. C'mon people, parent your kids! At what age do you turn people away? How do you handle it? I am dying to hear what everyone has to say about this.