Why does a minor start putting on tefillin before his bar mitzvah without saying a blessing?

As the tefillin have specific placement and need to be tied accurately, the minor may not do it correctly. Tefillin, inherently connected to the development of intellect, may not be fully developed in the minor to make a blessing. https://www.torahrecordings.com/rebbe/igroskodesh/011/008/3458