On Shabbat, at a reception subsequent to religious services where a young boy celebrated his Bar Mitzvah, may the Bar Mitzvah boy himself recite Kiddush on behalf of those in attendance?
This issue is not as simple as it may appear. The Rama rules that a young boy is presumed to be an halachic adult upon becoming a Bar Mitzvah at the age of thirteen. This position is contrary to the ruling of the Bet Yosef that contends that a young boy is not to be categorized as an adult until he has both attained the age of thirteen and developed two adult hairs. (Orach Chayim 55:5) The Rama’s position is that once a boy is thirteen years of age there is a presumption that he has developed two adult hairs. This presumption says the Mishna Berura is applicable only on laws of a rabbinic nature. To the extent that most boys develop adult hairs by the age of thirteen, on Mitzvot such as Tefila, which most rabbinic scholars contend is but a rabbinic Mitzvah, we accept the preumption that the Bar Mitzvah boy is an adult. On matters dealing with, however, Biblical Mitzvot, we are not to rely on any presumptions. On Biblical Mitzvot it is necessary to assess whether the young boy has in fact actually developed two adult hairs. (Mishna Berura-55:31) The rationale must be that on Biblical Mitzvot one does not rely upon a Hazaka or presumptions when it is possible to clarify the issue and resolve all doubts. Another way of viewing this is to contend that until the young boy manifests two adult hairs his maturity is a matter of doubt. On rabbinic matters doubtful issues are ruled leniently, and on biblical issues we are stringent on all matters of doubt. (Mishna berura 55:40) Kriat HaTorah is a rabbinic ordinance. Accordingly, one may presume that the Bar Mitzvah boy is an halachic adult and may, therefore, read the Torah for the congregation. Kiddush on Shabbat is a Biblical Mitzvah. As such, unless someone has actually verified that the young Bar Mitzvah boy has, in fact, two adult pubic hairs, it would not be proper for the Bar Mitzvah boy to make Kiddush for the assembled guests to enable them to observe the Mitzvah. Comparable logic would apply to the propriety of a Bar Mitzvah boy reading the Torah on Parshat Zachor, which most sages hold is a Biblical Mitzvah. Rabbi J. Simcha Cohen