I think Lisa is right. To a degree I believe that the teenage years are just a very anxious and unsettling time in your life and most of that is because your hormones have not leveled out.
I think that today there are also a lot of pressures that kids have to face that are very different from the pressures of the past. The pressures of the past were more global, the depression, wars, energy crisis. All of that was more probably very difficult to deal with but it was not things that affected the teenager themselves. The whole country or the world might be dealing with a big issue like the depression, but one kid today might be dealing with the fact that their mom or dad is a drug addict. One kid today might be dealing with name calling and being treated horribly in school everyday.
I guess I think that since we don't have as many huge global issues as they did in the past, that the issues of today's teenagers are a lot more personal to them. They effect their everyday lives.
I think the issue of media and hollywood is also in part to blame. Society's idea's about what is the perfect "look" the perfect "body" are unrealistic because of the influence of movies and television. Pressure to succeed in school and in the work place is stronger than I think it ever has been.
I just think there are a lot of factors that go into it and when you put them on top of a teenager who is probably a bit hormonal, it gets pretty complicated.