Millennials may be given a lot of grief for taking selfies all of the time, but this new study shows that youth violence is in dramatic decline. The study, conducted by researchers at Boston University, found a 29% decrease in violence related to young Americans between the years of 2002 and 2014. style=”display:inline-block;width:300px;height:250px” data-ad-client=”ca-pub-8420654331411867″ data-ad-slot=”1313712966″> “There…