Chinuch explains that nazirite vows take effect through substitute or incomplete expressions, impose the full prohibitions even when phrased conditionally, and may be annulled like other vows; a father may also impose neziros on his minor son until age thirteen and one day, but a mother may not.
וּמָה שֶׁאָמְרוּ זִכְרוֹנָם לִבְרָכָה גַּם כֵּן בְּעִנְיַן נְזִירוּת, דְּכָל כִּנּוּיֵי נְזִירוּת כִּנְזִירוּת, כְּלוֹמַר, מִי שֶׁהָיָה עִלֵּג אוֹ מְקוֹמוֹת שֶׁהַכֹּל עִלְּגִין וְדַרְכָּן לוֹמַר בִּמְקוֹם נָזִיר, נָזִיק אוֹ נָזִיחַ אוֹ פָּזִיחַ, וְאָמַר אֶחָד מִלְּשׁוֹנוֹת אֵלּוּ עַל עַצְמוֹ, כְּגוֹן שֶׁאָמַר אֱהֶא נָזִיק אוֹ נָזִיחַ אוֹ פָּזִיחַ הֲרֵי זֶה נָזִיר, שֶׁאֵין אוֹמְרִים בִּנְזִירוּת שֶׁיִּהְיוּ דִּבְרֵי פִּיו בְּכִוּוּן כִּלְבָבוֹ כְּמוֹ בִּשְׁבוּעָה, אֶלָּא מִכֵּיוָן שֶׁבִּלְבָבוֹ לְהִנָּזֵר וְאָמַר דְּבָרִים שֶׁיֵּשׁ לְהָבִין בָּהֶן שֶׁיְּהֵא נָזִיר, אַף עַל פִּי שֶׁהֵן מִלּוֹת שֶׁאֵין עִנְיַן הַנְּזִירוּת מוּבָן מִתּוֹכָן יָפֶה הֲרֵי זֶה נָזִיר. וְכֵן מָה שֶׁאָמְרוּ שֶׁיְּדוֹת נְזִירוּת כִּנְזִירוּת, וּמָה הֵן הַיָּדוֹת? כְּגוֹן שֶׁאָמַר אֱהֶא וְהָיָה נָזִיר עוֹבֵר לְפָנָיו הֲרֵי זֶה נָזִיר. אוֹ שֶׁאָמַר אֱהֶא נָאֶה וְתָפַס בִּשְׂעָרוֹ הֲרֵי זֶה נָזִיר וְכֵן הָאוֹמֵר הֲרֵינִי נָזִיר מִן הַחַרְצַנִּים בִּלְבַד אוֹ מִן הַתִּגְלַחַת, אוֹ מִן הַטֻּמְאָה בִּלְבַד הֲרֵי זֶה נָזִיר גָּמוּר. וְהָאוֹמֵר הֲרֵינִי נָזִיר עַל מְנָת שֶׁאֶשְׁתֶּה יַיִן אוֹ אֶטָּמֵא לְמֵתִים אוֹ אֲגַלַּח הֲרֵי זֶה נָזִיר וְאָסוּר בְּכֻלָּם, מִפְּנֵי שֶׁהִתְנָה עַל מַה שֶׁכָּתוּב בַּתּוֹרָה וּתְנָאוֹ בָּטֵל. וְנִשְׁאָלִים עַל הַנְּזִירוּת כְּדֶרֶךְ שֶׁנִּשְׁאָלִין עַל שְׁאָר הַנְּדָרִים. וְהָאָב מַדִּיר אֶת בְּנוֹ קָטָן עַד שְׁלֹשׁ עֶשְׂרֵה שָׁנָה וְיוֹם אֶחָד בְּנָזִיר, אֲבָל לֹא הָאֵם, וְדָבָר זֶה קַבָּלָה. וְהַגּוֹיִם אֵין לָהֶם נְזִירוּת, אֲבָל יֵשׁ נְזִירוּת בַּעֲבָדִים וּבְנָשִׁים. וְהַבַּעַל וְהָאָב מֵפֵר לָאִשָּׁה נֶדֶר נְזִירוּת כְּמוֹ שְׁאָר נְדָרִים, וְכֵן הָאָדוֹן אִם יִרְצֶה כּוֹפֶה לָעֶבֶד לִשְׁתּוֹת יַיִן וּלְהִטַּמֵּא [ה' נזירות פ"א].
[Also among the laws is] that which they, may their memory be blessed, said that all substitutes for the term of nazirite are effective — meaning to say, if a person had a speech impediment, or lived in a place where everyone has a speech impediment, and their way is instead of saying nazir, they say nazik, nazich or pazich and he said one of these expressions about himself, such that he said, “I will be a nazik, nazich or pazich,” behold, he is a nazirite. As we do not say that the words of his mouth must be identical to [what is in] his heart, as we do for oaths. Rather, once he has [decided] in his heart to become a nazirite and he says [something by which] it can be understood that [he wants] to be a nazirite — even though these are words that themselves do not [positively identify] him as a nazirite — behold, he is a nazirite. And so [too,] that which they said that [adjunct expressions are effective]; for example, where he says, “I shall be,” as a nazirite passes before him. Or if he says, “I will be beautiful” and holds his hair, behold, he is a nazirite. And so, one who says, “I will be a nazirite from grape seeds only,” or “shaving, or impurity only,” behold, he is a complete nazirite. And one who says, “I will be a nazirite on the condition that I will drink wine,” or “become impure,” or “shave,” behold, he is a nazirite, and all [the prohibitions of a nazirite] are prohibited to him; because [in the case of] one who makes a condition which violates the laws of the Torah, the condition is cancelled. One may request [annulment] on a nazirite vow in the same way that one requests on other vows. A father may make a nazirite oath for his son up until age thirteen, but the mother may not, and this thing is a tradition. Gentiles are not subject to [becoming a] nazirite, though women and slaves are. A husband or father may annul the nazirite vow of his wife or daughter like other vows, as may a master force his slave to drink wine or become impure. (See Mishneh Torah, Laws of Naziriteship 1.)
