10:24 If a boy below the age of thirteen knows how to take care of tefillin and can be trusted not sleep or pass wind while wearing them, then his father must buy tefillin for him to wear. The prevalent custom nowadays if for a boy to start wearing tefillin two or three months before he becomes bar mitzvah.
10:25 When it comes to wearing tefillin on Chol Hamoed, there are many opinions and many customs. Some communities follow the opinion not to wear tefillin on Chol Hamoed, while others do but without pronouncing the brachos audibly. (These people also do not wear tefillin publicly, through the streets to shul – see Mishnah Brurah 31:8.) Still other communities wear tefillin on Chol Hamoed without saying the brachos at all, keeping in mind that if tefillin ought not be worn on Chol Hamoed then they should be considered regular straps, i.e., not an attempt to fulfill a mitzvah that doesn’t apply. Even without saying the brachos, one may not interrupt between putting on the hand tefillin and the head tefillin, but one may respond to Kaddish and Kedushah. We should take care that we don’t have a situation where some in the congregation are wearing tefillin and others are not as this is considered divisive. (If one who does not wear tefillin on Chol Hamoed davens in a minyan where they do, he should put them on without a bracha – see Mishna Brurah 31:8.)