Our youngest just turned 12. She will probably Trick or Treat longer than 12 years, as her sisters did and the kids in this area often T or T well into High School.
She is not allowed to go alone. I have been on her a little to let me know who she wants to go with, so we aren't looking for someone to go with that day.
She usually goes with friends and maybe one parent. I think she is old enough to go with a bunch of friends and no parents, if they are home by dark. Twelve year olds are strange creatures, and she would want to die of embarrassment if I were standing there, with a bunch of 12 year old (some of whom are taller than I am) while they Trick or Treat. So, she can go with friends as long as they don't go far and are home by dark.
She's the youngest in a good sized family, so I gave up the "helicoptering" many many years ago. For us, a bit of safe, benign neglect is good for kids of a certain age.