, 28 November 2014 (UTC) 
 :"Wikipedia" isn't asserting the right to define anything.  Wikipedia is accurately reporting what published WP:Reliable sources say that the definition is, according to the agencies that have actually been using that definition, in some cases for more than a century, in all of these statistics.  If you don't like the definition, because it doesn't match up with your interpretation of the name, then your next step needs to be contacting several thousand government agencies and convincing them that a woman who gets pregnant the night before her 20th birthday ought to be counted as a "teenage pregnancy", rather than complaining that we're accurately reporting their definition. 
 :Your personal beliefs about the likelihood of a 20 year old being emotional mature are irrelevant.  When they made up this definition, the issue in their minds had nothing to do with emotions, and everything to do with medical complications and economic power.  In fact, they were concerned not about "teenage pregnancy" so much as they were concerned with "teenage motherhood":  It wasn't really about whether teens were having sex (because more of them were married or engaged to be married back then, so sexual activity was expected).  It was about whether they and their babies were going to live or die, and whether they would end up being charity cases.  (Also, they thought that 20 year olds were mature, and that even 16 year olds ought to be able to run a household on their own.  This was back when an 8th grade education was considered enough for most people, and when children were economically productive by age 10 or 12.)    02:45