My mother refused to give me a curfew when I was growing up. I wasn't allowed to go anywhere without an adult chaperone until I was old enough to drive anyway, but even then, she said "no curfew." She just told me to be home "at a reasonable hour." Each time I arrived home, she would decide if the hour was reasonable or not. She also wanted me to call and inform her every time I left somewhere or arrived somewhere else, though I interpreted that rule literally enough when going out to pick up friends that she told me to stop it in exasperation. I think it was still my sixteenth birthday.
The first time she assigned me a curfew was the summer after my freshman year of college. I had been living on my own in a big city far away, I was nineteen, I was working full-time to save up money for the coming school year, and I had finally started going on dates. She said my curfew was 9pm. If I wanted to go to a movie with friends or be out after dark, I "just had to ask."