Are Bedtimes for Teens Babyish?
Understand that you're not going to be able to change their sleep patterns, but you can negotiate a "bedroom time." And it should be approached as a negotiation, not a mandate -- you're more likely to get their cooperation if you do so. It's best to approach your teens at a time when they are relaxed, fed, and open to conversation.
Begin the discussion by saying something like: "Kids, I need the house quiet by 10:00 on week nights. If you're up talking on the phone, or watching TV, or fixing food in the kitchen, it makes it difficult for the rest of us to get to sleep. I realize that I can't control when you actually fall asleep, but I'd appreciate it if you would be in your bedrooms by 10:00 at the latest on school nights. What do you think about that?"
You'll probably be more successful in reaching a positive resolution if you shift the onus of the situation onto yourself rather than onto them. If you say, "I think you need to be in bed by 10:00 because it's good for your mental and physical health," your teens will most likely feel that you're babying them and are less likely to be open to the "bedroom time" suggestion.
Since this is to be an "open discussion," be prepared for comments like: "That's the stupidest thing I've ever heard! I don't want to be confined to my bedroom by 10:00." Don't get angry; just talk it out. Eventually you will get the "Okay mom, no problem" response you want.
If your teens are resistant, ask them what they think a reasonable time for them to check into their rooms would be and see if you can reach a realistic compromise. It's important that you make it very clear that you will enforce whatever time they agree to. Your teens should understand that privileges like use of the phone, and the computer, and control of the TV will be limited (even restricted) should they not keep up their end of the agreement.
Once you've all agreed to a "bedroom time" realize that you'll most likely need to remind them nightly when it's time to go to their rooms until they get used to the idea and go there on their own. Keep your reminders upbeat and brief for example; "It's 10:00, time to be in your bedroom."
It may be helpful to create some kind of nightly ritual that will entice them to go to their rooms, like preparing them a cup of soothing tea, or making it a time for a one-on-one chat with you about the day's events.