Perhaps in moderation and special occasions couldn't hurt. I see people giving kids iced coffee and iced cappuccinos before they're teens. I've even seen other ethnics give tots iced coffee, but that could be a cultural thing. I don't know.
I started drinking coffee on Saturday mornings when I was 15. It didn't stunt my growth or give me any other problems. But I jack up my coffee half full of milk and a few tsp of sugar.
I agree with TN, it's not the healthiest thing and, yet, we still load them up on high caffeinated, sugary pop, or "liquid candy" as some dieticians like to call them. Those have more sugar and caffeine than a cup of coffee. At least sugar is amount is controlled to your preferred taste and dietary limitations.
If you are concerned about the caffeine, then you can opt for decaf.
But don't get yourself down about letting your teen drink coffee sometimes.
What you do need to worry about is those energy drinks, which can have a dangerous amount of caffeine even for adults.
Perhaps a talk with your teen about the dangers of caffeinated drinks can go along with the talk about the dangers of alcohol and drugs.
And another suggestion could be to educate yourselves about what caffeine really is and where it comes from. The more you know the better.
I just looked up kids and caffeine on Google and the first thing I got was this brief but informative, kid/parent friendly article:
http://kidshealth.org/parent/growth/feeding/child_caffeine.html[/URL]