You Can’t Have It Both Ways
‘A Minor Who Reaches Maturity’
Our Gemara familiarizes us with one of the basic elements in the Babylonian Talmud: Rava’s chazakah.
As we know, only an adult must keep the mitzvos. But who is an adult? Every male above 13 and every girl above 12 provided that they possess physical signs of maturity. Rava posits that a 13-year-old boy is considered an adult even without confirming that he has signs of maturity because of the chazakah that he is like most people his age, who have these signs.
Rabbinical vs. Biblical
According to halacha (Rema, Orach Chayim 55:5; Magen Avraham, s.k. 7; Mishnah Berurah, s.k. 31 and 40; Rema, 199; Magen Avraham, s.k. 7; Mishnah Berurah, s.k. 27), we can rely on Rava’s chazakah for rabbinical decrees but not biblical halachos. Thus, a boy who just turned 13 can automatically be counted in a minyan since the requirement of tefillah b’tzibbur is rabbinical (Rema and Mishnah Berurah, Orach Chayim 55). For the same reason, he may also be a shaliach tzibbur and lead bentching. He may not, however, blow shofar or say kiddush for an adult, for example, since the mitzvos of shofar and kiddush are biblical (see Bi’ur Halachah, 271:1).
May he blow shofar or say kiddush for another 13-year-old boy who has not been checked for simanim. Rabbi Efrayim Zalman Margaliyos, zt”l (Mateh Efrayim 589:7), discusses this question and asserts that he may not.
A Doubt of a Doubt
At first, it seems like we have a doubt of a doubt (sfek sfeika) at hand, which should yield a lenient ruling. The blower may be an adult, and even if he’s a minor, the person he’s blowing for may also be.
However, Tosafos (above, 29a, s.v. “Teisheiv lezachar”) says sfek sfeika does not apply to this case since it would lead to two contradicting leniencies. How so? Suppose after listening to his friend blow shofar, the second 13-year-old boy wished to say Shema for him. Based on sfek sfeika, he should be able to. He may be an adult, and even if he isn’t, his friend (who blew shofar for him) may be a minor, too. It turns out that sometimes we’re assuming the blower is an adult and his companion a minor and sometimes the opposite. Thus, sfek sfeika does not apply to this case (see Turei Even, Rosh Hashanah 29a, s.v. Tumtum and see Halachos Vehalichos Bar Mitzvah, p. 43).