1) THE AGE AT WHICH A "SERIS" IS CONSIDERED A "GADOL"
OPINIONS: The Gemara concludes that a Seris who reaches "20 years of which 30 days have passed" is considered to be 20 years old and is an adult, a Gadol. This is in accordance with the ruling of Rebbi Yosi ben Kiper in the name of Rebbi Eliezer (47b).
To exactly what time does this refer?
(a) Most Rishonim explain that this refers to a person with Simanei Seris who reaches the age of 19 years and 30 days.
(b) The RAMBAM (Hilchos Ishus 2:5) rules that at 30 days before the age of 20, a Seris is considered a Gadol. (The RA'AVAD disagrees and contends that after 19 years and 30 days, the Seris is considered a Gadol, like most other Rishonim rule.)
The TUR suggests that there is a printer's error in the text of the Rambam. The MISHNEH L'MELECH, however, rejects this suggestion. He points out that the Rambam reiterates his ruling of 20 years less 30 days no less than three times in the same chapter, and thus it is very unlikely that this is a printer's error.
The Acharonim explain that it is possible to read the words of the Gemara in accordance with the Rambam's ruling. Instead of interpreting the words as "20 years of which 30 days have passed," the words may be saying, "20 years from which 30 days are lacking."
Why does the Rambam explain the Gemara this way, and not in the more straightforward way of the other Rishonim? The BACH (EH 172:5) explains that the Rambam was bothered by a question: If the Gemara means that 19 years and 30 days is considered 20 years because 30 days count as an entire year, then why are 30 days necessary? A single day should suffice, because even one day into the year is considered a year, as the Gemara says in Rosh Hashanah (2b). The Rambam therefore understands the words of the Gemara differently.
(The Bach points out that there are other laws in which 30 days before a year is already considered the beginning of the following year, such as the law that it is forbidden to plant within 30 days of the Shevi'is year.)
2) UPPER AND LOWER SIGNS OF ADULTHOOD
QUESTION: The Mishnah states that if the lower sign of physical maturity of a female appears before the upper sign (see RASHI DH Bo, DH ha'Elyon, and 47a, DH Bochel), she may do either Chalitzah or Yibum. Rashi (DH O Choletzes) explains that since she possesses lower hairs, this is a Siman Muvhak, a clear sign, that she has reached adulthood.
The Mishnah continues and says that if the upper sign appeared before the lower sign, "even though this is impossible," Rebbi Meir rules that she may do neither Chalitzah nor Yibum, because she is still a minor. The Rabanan disagree and maintain that she may do either Chalitzah or Yibum. Rashi (DH Aval) explains that according to the Rabanan, if the upper sign appears before the lower sign, it is because the lower hairs actually appeared first but afterwards fell off.
The Gemara questions the view of Rebbi Meir. Why does the Mishnah say that it is impossible for the upper sign to appear before the lower sign if we indeed witness that this happens? The Gemara answers that it is only the Rabanan who maintain that it cannot happen; Rebbi Meir maintains that it can happen. The Gemara proceeds to explain that the reason why the Mishnah states that, according to the Rabanan, it is impossible for the upper sign to appear before the lower sign: had the Mishnah not said that it is impossible, we might have thought that most women produce the lower sign first, while a minority indeed produces the upper sign first. If indeed a minority produces the upper sign first, then we might have thought that the reason why Rebbi Meir maintains that the woman in such a case is still a minor is that Rebbi Meir is always concerned for the minority. A woman who produces the upper sign before the lower sign might be from the minority for whom this is a natural phenomenon, but she is not yet considered an adult because the Halachic sign of adulthood is the lower hairs alone. The Rabanan, in contrast, are not concerned for the minority, and thus they would rule that we may assume that the lower hairs actually developed but then fell off.
The position of Rebbi Meir seems difficult. The reason why a minor girl may not perform Chalitzah or Yibum is that it might transpire later that she is an Ailonis (see Bartenura). The Gemara in Yevamos (80b) states that one of the signs of an Ailonis is that she does not have nipples. Other signs of Ailonis are mentioned, and Rav Huna there rules that she is not an Ailonis unless she possesses all of the signs. (TOSFOS in Kidushin (4a, DH d'Lo) says that Rav Huna's statement presumably refers both to the male Seris and to the female Ailonis, and if either one possesses one positive sign of maturity, he or she is not in the category of Seris or Ailonis.) Accordingly, since the Mishnah is discussing a case in which she possesses the upper sign (of "Bochel," nipples), even Rebbi Meir should agree that she may perform Chalitzah or Yibum because there is no longer any concern that she might be an Ailonis!
ANSWER: REBBI AKIVA EIGER answers that when Rav Huna states in Yevamos (80b) that one is an Ailonis only when she possesses all of the signs, he means that she is a definite Ailonis only in such a case. When, however, she possesses one of the signs of an Ailonis, Rav Huna agrees that there is a doubt and she might be an Ailonis, even though she possesses some signs of maturity which an Ailonis normally does not have.
Therefore, in the case of the Gemara here, even though the girl possesses the upper sign of "Bochel" Rav Huna agrees that this is not sufficient evidence that she is not an Ailonis, since she does not yet possess the lower sign of adulthood. Rebbi Meir maintains that the girl may not perform Chalitzah or Yibum because there is a minority that may still be an Ailonis, and Rebbi Meir is always concerned for the minority. (D. BLOOM)
3) THE HALACHIC SIGNS OF MATURITY
OPINIONS: The Mishnah and Gemara discuss at length the signs of physical maturity. One such sign is the appearance of two pubic hairs, which are considered a Siman (sign) of maturity for Halachic purposes. Before the growth of such hairs, a person has the status of a minor whose intellectual capacity has not yet matured.
Is the growth of hair a causal factor of intellectual maturity, or merely an indicator that maturity has been reached? While the growth of hair does not seem to be physiologically correlated with mental maturity, it is possible to understand that the presence of two hairs is merely a physical indication that the child is physically mature, and therefore presumably also mentally mature (and such a presumption suffices, according to the Torah, to give him a Halachic status of an adult). It is also possible to understand that the Torah dictates that no matter how intellectually mature a child may be, he is not considered a "Bar Da'as" according to Halachah until he has two pubic hairs, because the presence of two hairs in some way bestows upon him the status of adulthood. Are the hairs merely a sign ("Siman") that the child has reached Halachic maturity, or are they in some way a cause ("Sibah") of Halachic maturity?
(a) The MAHARIT (Teshuvos 1:51) writes that the growth of hairs does not bring about Halachic maturity. It is merely a sign that the child has matured. The Maharit points out that this is consistent with the meaning of the word "Siman" which the Chachamim use to describe the hairs.
This is also the view of RABEINU CHANANEL (quoted by the ROSH, Gitin 9:11), who writes that we lack the proficiency to determine Halachic maturity based on the mental acuity of a child. Therefore, we must rely on the Simanim to determine when he or she has matured. Rabeinu Chananel implies that if we would be able to determine the mental acuity of a child without having to rely on Simanim, it would be possible that a child would be considered an adult even before the Simanim appear.
(b) The SHITAH MEKUBETZES in Bava Basra (56b, DH v'Li Ani) writes that the Simanim actually bring about the Halachic maturity of a child in a causal way, and they are not merely incidental indicators of maturity.

48b----------------------------------------48b

4) RELYING ON THE TESTIMONY OF A WOMAN WITH REGARD TO A PROHIBITION
QUESTION: The Gemara cites a Beraisa in which the Tana Kama says that the examinations performed to determine whether a girl has reached physical maturity may be done by a woman, and we may rely on the woman's testimony regarding the girl. Rebbi Eliezer relied on his wife to perform such examinations and to report the results, and Rebbi Yishmael similarly relied on his mother.
Why is the testimony of a woman accepted in such cases when, in almost all other cases, Beis Din does not accept the testimony of a woman?
ANSWERS:
(a) The CHIDUSHEI HA'RAMBAN explains that the reason why women are believed with regard to whether a girl has reached adulthood is that the girl's maturation is an easily verifiable fact. Therefore, we accept the testimony of a woman in such a case.
The Ramban gives another example in which we rely on witnesses whose testimony ordinarily is not acceptable. The Gemara in Yevamos (39b) explains that Beis Din must verify that the person brought before them to perform Chalitzah is indeed the brother of the deceased husband. The Ramban points out that the Halachah is that a woman, and a close relative of the man doing Chalitzah, are believed to say that he is the brother, even though they are not valid witnesses in almost all other cases. The Ramban cites the RIF in Yevamos (13a of the pages of the Rif) who explains that the witnesses are merely revealing that the man is the brother and that the woman is the widow, and they are not giving testimony about a question of Isur or a monetary matter.
The Ramban writes that in the case of the Gemara here, another reason to accept the testimony of a woman is that the girl is present and it is easy to determine whether she possesses the signs of adulthood. In such a case, a woman is believed to say that the girl is an adult, whether lenient or stringent ramifications will result from her testimony.
The Ramban rules that the Halachah follows the Tana Kama.
(b) However, the Ramban gives a different reason for why we may rely on the testimony of a woman, according to the Tana Kama. During the girl's twelfth year, a woman is believed to testify about the girl's physical maturity only for matters of stringency, just as she is believed for matters of stringency before the girl has reached her twelfth year. The Tana Kama agrees with Rebbi Shimon with regard to this point.
After the girl has passed the age of twelve, a woman is believed to testify about her physical maturity only because at this age, according to Rava, there is a Chazakah that the girl already has the signs of adulthood, and the woman's examination is necessary only to provide support for that Chazakah.
The Ramban cites the Rif in Yevamos (40b) who rules in accordance with this approach.
(c) The HAGAHOS ASHIRI in Chulin (to the ROSH 1:14) writes that although there is a rule that one witness is not believed when there is a Chazakah that the item is forbidden (and, therefore, since until now we knew that the girl was a minor, we should be required to assume that she is still a minor and is not permitted to do Chalitzah), this refers only to the testimony of "empty, hasty" people. Even though the Torah accepts the testimony of two people of this sort (as long as they have no specific disqualification), one witness like this is not believed against a Chazakah of Isur. However, one trustworthy and decent witness is reliable. This is why Rebbi Eliezer relied on his wife and Rebbi Yishmael relied on his mother.
The Hagahos Ashiri adds that even the opinions in the Beraisa that disagree with the Tana Kama refer only to the testimony of ordinary women. They agree that exceptional women, such as Rebbi Yishmael's mother who was well-known for her integrity, may be relied upon for this form of testimony. (See also TESHUVOS REBBI AKIVA EIGER 1:7, DH v'Hineh b'Inyan, and TESHUVOS ACHI'EZER 1:5:8.) (See also Insights to Kidushin 78:1.) (D. BLOOM)

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