Stress is a part of life. There is no way to eliminate stress completely for any particular age group, gender, or just any individual in general. Stress stems from many aspects and elements of human life. To take away stress is essentially to take away life from humans completely.
In teens, stress can come from school, family, college applications, clubs, friends, boyfriends/girlfriends, finding who they are, finding what they want to do/be when they grow up, and basically everything that they do and everyone they have ever had connections with. So to stop teens from having stress, we'll have to get rid of all those things. This pretty much takes away everyone they know and everything they do. I don't know about you but that isn't much of a life to me.
We can, however, reduce some negative stress. Stress can serve as a positive thing like motivators that push us to do great things. But it can also be negative and bring us down. To reduce the stress for teenagers, we need to pinpoint what types of stress are generally bad and minimize the intensity of the sources of those stresses. Although if we do that, there is a great risk of new stresses arising from somewhere else whether we want to or not. For instance, let's say that being in relationships as a teen can cause a lot of negative stress. We try to reduce this by not allowing teens to be in relationships. Then a new stress would arise from this because now teens lack freedom and feel more pressured. I'm not saying that this is true, but I'm just trying to point out that reducing some stresses may cause the rise of new ones.
So what I'm trying to say is that we can't eliminate stress and reducing stress isn't going to help all that much. Rather than focusing on the stress, we should focus on people and teach people how to deal with stress. If each person can deal with stress better, the amount of stress felt in every individual would automatically reduce anyway as a positive repercussion (if repercussions could be positive).