You said, "I've had grown adults come to my house trick or treating at Halloween and thought this was odd."
Adults like candy too! Isn't there a child in every adult? Let that "kid" express himself for crying out louder than we usually do! :D
When I think about the walking bags of pus, the hideous skeletons on little black costumes, knives in bloody heads, a little princess who can get killed, Jason and his boys, and the other horrible, slimy creatures, I realize that all of them are the epitome of horror/fear, death, murder--just a big, nasty celebration that is topped off with pleasure relief: CANDY, and later a bloody, murderous movie like "The Chainsaw Murders." These parents who subject their kids to this are among those who advocate for non-violence, gun control, getting rid of devil worshippers, and parents against drunks who cause victims to look like the things their kids "celebrate."
Some people poison and even kill kids with tricky treats. Some get killed while crossing crowded streets. Some are frightened to death when they are tricked.
Their dangling eyeballs costumes end up all over someone's lawn.
Now, what was that question--"What age should they stop trick or treating?" I think that the policemen, parents, volunteers, and the National Guard should trick or treat with these kids to monitor and protect them, and they should be rwarded with more than candy. Those who volunteer to x-ray candy should be paid overtime along with the other big trick or treaters. Parents, poor souls, just have to settle for taking the kids to counseling when it is all over.
I truly think that big kids and adults are the only ones who can come out of it unscathed because they know that this is all fabrication designed for frightening fun. Well, almost.
I took my grandkids to the local grocery store one time for "fright night." I left running ahead of them when I saw Jason and another monster come after us with hamburger meat for brains. I think one of the bag boys found me near my car and brought the screaming kids to me. Hey, I am a kid at heart, OK? I wonder why they won't give trick or treaters my age sugar-free candy!
Oh, "What age?" My answer: 70. :D
Enough said. I had fun responding! I have a hub idea and hope others got one too.