http://www.aafp.org/afp/2015/0315/p372.html http://www.aafp.org/afp/2015/0315/p372.html http://www.aafp.org/afp/2015/0315/p372.html http://www.aafp.org/afp/2015/0315/p372.html [aafp.org] 15 to 24 years