I trick or treated up to and including my senior year of high school. I was 17 that Halloween.
Mentally, I suppose, my guideline is Trick or Treating is acceptable, (out in a regular, non-college town neighborhood, for yourself) until you reach the age where you would technically be in college. Usually you will be 18 or older at that point. Once college age, Trick or Treating in neighborhoods (or dorms) with a lot of other people about the same age as you is fine, if they are doing it. Taking younger kids out Trick or Treating in a regular, non-college neighborhood and accepting candy if you are offered is fine. I feel funny about college age kids ASKING for candy in a regular, non-college oriented neighborhood. But it would also depend on the kid and the circumstances, I guess.
My rule is 1 piece of candy per person, and they must have at least made an attempt at a costume.
Now, adults of ANY age in costume, out Trick or Treating with their kids, or adults that I know personally, get offered candy.
I love the holiday, and am doing what I can to encourage more Trick or Treaters to come to our neighborhood.
We've also seen Halloween as a great time for us to see people that we don't always see the rest of the year. For many years, I've made the trek back to my hometown, and taken MY kids Trick or Treating there, just so I could get a chance to say hi to people I've known since my child hood. They've watched me, and now, my kids, grow up, that way. We haven't done it the past 2 years, and I always have a tinge of sadness about it.