I live in a suburb, lots of different types of neighborhoods within a few miles of each other. Lots of people come into my neighborhood to trick or treat. Most of the homes on my side of the block decorate and hand out candy.

I do not give candy to anyone who is clearly and adult, dressed or not. I also tell them, that I don't give candy to adults. For example a group of kids under 12 all dressed up, then the mom or aunt or grandma who is dressed puts their bag out, they usually (in my neighborhood) clearly pushing 40 or older. I tell them Halloween Trick or Treat candy is for the kids. I've done this for the last 7 years in my current home, I've yet to have anyone confront me about it.

Older teenagers in my neighborhood usually put effort into their costumes, I always compliment their costumes and give them candy.
People in their early 20's, well it's hard to tell their age so they probably get candy from me too.

I also tell the older kids that have no costume, to put some effort into it.

I know this sounds mean to some, sorry.