Gemara

Question: What do we learn from "Ish Ki Yafli (Neder b'Erkecha)"?

Answer: It includes a Mufla Samuch l'Ish (a minor close to adulthood. He can vow Erchin, i.e. to give money to Hekdesh, based on a person's age and gender.)

Question: This is like the opinion that vows of such a child are mid'Oraisa. According to the opinion that they are mid'Rabanan, what does the verse teach?

Answer: It includes a Nochri Mufla Samuch l'Ish. This is like the opinion that a Nochri can pledge Erchin.

Nidah 46b (Rav Huna): If a Mufla Samuch l'Ish was Makdish something and ate it, he is lashed. It says "Ish Ki Yafli Lindor Neder," and "(Ish Ki Yidor...) Lo Yachel Devaro" -- whoever is an "Ish" for the former (his vows take effect) is an Ish for the latter (he is liable for transgressing them), and vice-versa.

Support (Beraisa) Suggestion: A minor is like an adult regarding intentional transgression of oaths, Isar (a way of vowing or swearing) and Lo Yachel.

Inference: A minor is lashed like an adult regarding Isar and Lo Yachel!

Answer #1: No, he is like an adult regarding the Isur of Lo Yachel, but he is not lashed.

Question: If Mufla Samuch l'Ish is mid'Oraisa (and it is forbidden even to him), he should be lashed. If it is mid'Rabanan, he should not be forbidden (Chachamim do not forbid minors)!

Answer: Chachamim commanded the one who supervises the minor to stop him from transgressing. (This is unlike R. Pedas, Yevamos 113b.)

Answer #2: No. The case is, the minor was Makdish and adults ate it.

Question: This is like R. Yochanan and Reish Lakish, who say that adults are lashed for (benefit from) a minor's Hekdesh. Rav Kahana says that adults are not lashed for a minor's Hekdesh. How can he answer?

Answer: He is lashed mid'Rabanan. "Ish Ki Yafli" is only an Asmachta.

Question (R. Yirmeyah - Beraisa): If an orphaned girl (who was married mid'Rabanan) took a vow, her husband can annul it.

If vows of a Mufla Samuch l'Ish are mid'Oraisa, how can he annul them? Mid'Oraisa she is not his wife!

Answer #1 (Rav Yehudah): Even if the vow is mid'Oraisa, Chachamim authorize him to annul. She is a minor, so Beis Din need not stop her from transgressing.

Answer #2: A woman vows on condition that her husband will consent. (Even if the marriage is only mid'Rabanan, she considers him to be her husband.)

Question (Abaye - Beraisa - R. Yehudah): If a minor did not bring hairs, if he separates Terumah, it does not take effect;

R. Yosi says, it is Terumah only if he reached Onas ha'Nedarim.

We are thinking that R. Yosi holds that (the obligation to take) Terumah is mid'Oraisa nowadays (after the Churban). If Mufla Samuch l'Ish is mid'Rabanan, how can Terumah mid'Rabanan exempt Tevel mid'Oraisa?!

Answer: R. Yosi holds that Terumah is mid'Rabanan nowadays.

Mishnah (Terumos 1:1): There are five kinds of people who cannot take Terumah, even b'Di'eved. A Cheresh, lunatic or child...

Mishnah (3): (This refers to) a child who did not bring two hairs;

R. Yehudah says, his Terumah is Terumah.

R. Yosi says, it is Terumah only if he reached Onas ha'Nedarim.

Rishonim

Rambam (Hilchos Nedarim 11:4): Once a minor reaches the years of adulthood, his (or her) vows are valid mid'Oraisa. This is even if he did not bring two hairs and is not an adult for other matters. His vows are valid, but he is not lashed for transgressing them or for swearing falsely until he matures and brings two hairs.

Rambam (Hilchos Nezirus 2:13): If a minor reached the age of vows and vowed to be a Nazir, he is a Nazir and brings Korbanos even though he did not bring two hairs and is not an adult for other matters.

Ra'avad: According to the opinion that Mufla Samuch l'Ish is mid'Rabanan, how can he bring a Chatas? It is Chulin b'Azarah! Perhaps the Halachah is that Mufla Samuch l'Ish is mid'Oraisa, like R. Yochanan and Reish Lakish against Rav Kahana.

Question (Tosfos Nidah 46b DH Iy Amarta): How did Abaye try to prove from R. Yosi that Mufla Samuch l'Ish is mid'Oraisa? In the same Beraisa, R. Yehudah holds that the Terumah is invalid, i.e. because Mufla Samuch l'Ish is mid'Rabanan and Terumah nowadays is mid'Oraisa!

Gra (YD 331:78): Our text of the Gemara is wrong. In the Mishnah, R. Yehudah says that the Terumah is valid. However, we can ask this question from the Stam Mishnah, which holds that the Terumah is invalid.

Answer (Tosfos): R. Yehudah holds that Mufla Samuch l'Ish is mid'Oraisa, but not to be lenient (to say that a child's separation permits the Tevel).

Poskim

Chasam Sofer (317, cited in Pischei Teshuvah 320:4): There are no Shi'urim regarding Nochrim, except for Erchin and Nedarim. We learn from "Ish Ish" that also a Nochri who brought two hairs can be Ma'arich, and we exclude Mufla Samuch l'Ish.

Shulchan Aruch (331:33): If a child reached the age of vows, even if he did not bring two hairs and become an adult, if he took Terumah, it is Terumah.

Shach (63): This is even for Terumah mid'Oraisa, since his vows and Hekdesh are valid mid'Oraisa.

Rebuttal (Gra 78): This is like R. Yosi. The Halachah follows the Stam Mishnah that says that a child cannot take Terumah even b'Di'eved. The Reisha of Mishnah 3 explains that this refers to any child who did not bring two hairs. Even though we hold that Mufla Samuch l'Ish is mid'Oraisa, and in any case Terumah is mid'Rabanan nowadays, Tosfos says that Mufla Samuch l'Ish is a stringency, not a leniency.

Shulchan Aruch (OC 343:1): If a child is eating Neveilos, Beis Din is not commanded to stop him.

Rema: Some say that after he reached Chinuch (training in Mitzvos), we must separate him. Some say that Chinuch does not apply to Beis Din.

Rashba (cited in Beis Yosef DH v'Chosvu ha'Tosfos): In Nidah, the Gemara asked how a mid'Rabanan husband can annul vows of a Mufla Samuch l'Ish if they are mid'Oraisa. It answered that Beis Din need not separate a child from Isur. This shows that this opinion is lenient even for a Mufla Samuch l'Ish. However, perhaps Chinuch applies only to Mitzvos Aseh.

Ketzos ha'Choshen (188:3): Rashi (Bava Metzia 71b DH Katan) says that a minor cannot make a Shali'ach because he cannot take Terumah. This is difficult, for a Mufla Samuch l'Ish can make Terumah, and this is mid'Oraisa! The Rambam (Hilchos Gerushin 6:9) says that a minor cannot make a Shali'ach to receive her Get because this requires witnesses, and we cannot testify about a minor, for her Da'as (intellect) is not complete. The Ra'avad learns from "Gam Atem" (written regarding Terumah) that a Shali'ach must have Da'as, just like the one who authorizes him. He and Rashi hold that no minor can take Terumah, for Mufla Samuch l'Ish is only mid'Rabanan. The Rambam holds that it is mid'Oraisa, so a minor can take Terumah, therefore he needed a different source that a minor cannot make a Shali'ach.