If your area has a legal curfew for teens, I would say that's a reasonable time for you to expect him to be home.
I had a curfew at his age - I wasn't supposed to go out on school nights, and when I went out with friends on weekends, I was to be home by midnight. My parents were pretty flexible about it. I babysat, and it was understood that if I was babysitting, the parents I was working for would get me home, and my folks wouldn't worry about when that happened. If I was out with friends, I could call to request an extension of my curfew for a specific purpose - "we're at _____'s house, can we stay to watch all three Star Wars movies?" I never asked for an extension I didn't get, but I was also smart enough not to ask for extensions that didn't involve specific times and places, and groups of people my parents knew.