You are putting me on, really? :rolleyes
The point which you do not recognize is that a mother is typically older. Cougars are the oldest and are purely the initiators of the sexual rendezvous... but we are not talking cougars, we are talking MILFS. I am fully aware that females hit puberty from anywhere from 12-14, younger in some instances. However, they are not typically seen as mothers. What you are trying to do is make the exception into the rule and it does not work. It loses the meaning.
If you are thinking of tagging your friend's Mom you are having a MILF experience. That is the basis of the expression.
Sure while it may be humorous to cite young women who have had children for a little blog post, factually it does not change the base of what a MILF is to those who know the term.