From the Mishna B'rura's introduction to the rules of Shabas: …But by what means can we arrive at this level: that one keeps Shabas in all its details? The advice on this is that one urge himself ...
Are there any mitzvot that kids under bar/bat mitzvah are obligated to keep? (not including for "educational purposes")
Common practice is that a boy begins wearing Tefillin when he reaches Bar Mitzvah age, or perhaps a month (or three) prior. While there should be an obligation even earlier (under the rubric of ...