I figure that you should be able do it until you feel like dressing up is stupid, or until you’re old enough to live on your own, whichever comes first.
Note, though: in my town, we get crappy weather on Halloween. Always. So, even when I was a little kid, I sometimes didn’t have a visible costume (what with my thick coat on and all).
When I was about 20 or so, I still loved to dress up, but didn’t need candy. So, I would get into costume and take my little neices and nephews trick-or-treating. I got lots of candy offered to me, but didn’t take it. I just enjoyed the experience of taking them!
You better be a kid if you stop at my door. Adult WITH children will most likely get candy. But teenagers will get a lecture on stealing from children… and don’t vandalize my place I WILL call the cops.
So say a 19-20 year old came up to your door with some pretty decent costumes. Very obvious they put effort into it. You wouldn’t give them any candy at all?!
I always figured door-to-door trick-or-treating should end when the kids turned thirteen or so . . . unless, of course, it was an adult taking the little ones around. Plenty of other kinds of Halloween fun for teens and adults.
Whatever the age, only those in costume should get candy. Yeah, I wuss out when confronted with a gang of sullen uncostumed 17 and 18 YO’s who’re bigger than I am and know where I live but it should be any age as long as they’re costumed.
No, I’m not in the habit of opening my door to adults wearing masks or disguises. How do you know they’re trick-or-treaters?
Why can’t people dress up and hand out candy? I did that a few times.
Because it’s Halloween! 
I’m not much for trick or treating, but that’s just because I was never that interested in it to begin with. However my girlfriend, who really is very sweet, nice, and all that, loves it. This year she plans to do it again, and will be turning 20 about a week after Halloween. I mean, it’s not really the candy that she wants, it’s the experience, but by denying her the candy because she’s ‘too old’ or something to that extent would put an extreme damper on her fun. If someone else is enjoying themselves, why would you try and stop them from doing so?
I’ll give anyone candy if they make the effort to dress up. I always dress up to give out the candy so I think people should at least try. Last year I had a surly 18 year old in normal clothes stop by. I told him he had to do something to impress me for his candy so he did an elaborate dance and claimed he was in a boy band. He got a big handful for the effort. Sometimes I think the surly teens are just trying to hide the fact that they are just as excited about the treats as the little ones are. Other times I just think “Get out of my yard you surly bums!”. I get too excited about Halloween, what other night can you dress up like a monster and have people give you stuff for it? Older and wanting candy? Come to my house, I’m the lady with the fog machine, the strobe lights, the scary music and all the good candy.
I last trick-or-treated at age ten. It was a warm night and I got all sweaty, traipsing around the apartment complex in my costume (I no longer remember what it was).
When I was younger, though, I loved it! When else would I get to wander around the neighborhood alone after dark, and see into strangers’ houses? 