My DD is only 14, but as she grows, I plan to give her curfews like I had when I was a teen.
I had curfews as long as I was in school. They differed depending on the time of year. During the school year, I always had to be home by 9 on weekdays. During the summers, or on weekends, it was based on age. When I was 16, curfew was midnight. When I was 17, it was 12:30, when I was 18, it was 1:00. Only exceptions were if I was working a job that required me to be out later, or if we were going to the drive-in movies. Our drive-in starts the first film at full dark, which isn't till 10-ish in the summer, so if we stayed for both shows it was expected that we wouldn't be home till 2-ish.
After I graduated, but when I was at home (summers, holidays, etc), I did not have a curfew, even though I was still 18. It was requested, however, that I be thoughtful of others in the home. My mom was a light sleeper, and if she had to work the next day it was hard on her to be woken up at 3 AM by people tromping in and out of the house, so I always tried to be home at a reasonable hour. If, for some reason, that wasn't possible, I would call her earlier in the evening and let her know I would be staying a friend's house.