Halloween

I was just wondering if there is an age limit on trick or treating in your areas. I live in a small town and it seems even high school kids get dressed up and go trick or treating. The town hasnt had any trouble with the older kids doing things to the younger kids but it just seems odd that they would still want to trick or treat. I always thought it was for the little ghost and goblins to have fun to dress up and enjoy there evening. But it seems more and more older kids are doing it as well. Any other people get older kids at there houses?