I would not suggest Colorado for a group of teenagers. Not because it is not a beautiful and enjoyable place to ride, it is. At least the mountain areas to the west. The east of Colorado is kind of bleak. But because it is a very hard place to ride if you are not in very good condition before the ride starts.
I'm making the assumption these teenagers are not avid cyclists who ride 5,000 or so miles a year at a fast pace. Unlike most other parts of the country, its very hard to sort of just ride along when climbing mountains. You can't just soft pedal and go slow. Most folks hard pedal and go slow up the mountains for hours. You really need to be in good shape before you start to keep the ride from being unpleasant and a daily torture.
Colorado also has very few towns in the mountains. So on many days you may only have one place to stop for food/drink on a 70-80 mile ride. Or no place to stop during the day. You really need a support vehicle along, or be able to support yourself, which requires you to be a fast cyclist not needing support or an experienced cyclist who knows what to do. Teenagers probably don't fit this.
Colorado riding also requires a full set of winter clothes for mountain riding. You have to carry them along with you to not risk ending up dead, literally. Probably not for teenagers, unless you have a support van or two or three right alongside the riders on each climb.
Colorado cycling also requires a triple as far as I'm concerned. Your cyclists may not have the right bikes for Colorado riding and the cost of getting the right gears may be a detterent.
Now with all this said, you can do a Colorado ride with inexperienced, not strong, riders if you plan correctly. Support vehicles and very short days and picking up riders and hauling them into the overnight towns. Your own meal, sag stops, from a support van.
I'm a fairly experienced cyclist. I did Pedal the Peaks week long ride in Colorado in 2002. I had minimal mileage and conditioning before the ride start. I thought I could get by since I had lots of experience. I made it, but it was not really enjoyable struggling up each mountain climb each day. I bought a triple crank and derailleurs specifically for the ride so I had almost a low enough gear. This year I did the Triple Bypass ride. Based upon my 2002 ride I was sort of fearing it. But I was in very, very, very good condition before the ride this year. It was sort of challenging, but not difficult. Even though it was in the 40s and rain for the first 80 miles and 2 passes. I had almost full winter clothes on. Places to stop for food/drink were pretty minimal except for the official sag stops.