When should a child begin laying tefillin?

Shulchon Aruch rules that once a child has the maturity to adhere to the necessary standards of cleanliness while wearing tefillin, he must be trained to wear them. Rema says that it has become customary for children not to wear tefillin because it can be assumed that children will not maintain those standards. Nonetheless, it has become conventional for a boy to begin laying tefillin a short time before he becomes a bar mitzvah. Customs differ as to when exactly he should begin, ranging from one month to three months before his birthday.

May women wear tefillin?

A woman is exempt from time-bound mitzvos, though she may choose to perform most of them if she wishes. Tefillin, however, is an exception. It is appropriate to protest if a woman chooses to wear tefillin. Some Rishonim explain that it is a degradation for one who is not obligated in the mitzva to wear a holy object like tefillin.

[סימן לח, סעיף ג; ביאורים ומוספים דרשו, 9

Who should put on tefillin immediately before Kriyas Shema?

A person who cannot maintain the necessary standards of cleanliness is exempt from laying tefillin. Due to his condition, he is actually forbidden from being “stringent” and wearing tefillin. If he can control his bodily functions for a short period of time, he should put on tefillin immediately before Kriyas Shema and remove them when he is finished. He may recite the brocha on tefillin between the brocha of Ahavah Rabah and Kriyas Shema. If he can stay in control until after he finishes Shemoneh Esreh, he should continue wearing tefillin until then.