Minimum Age of Cattle to be Offered
Requires Beit HaMikdash
VaYikra 22:27 An ox, lamb or goat, when it is born, shall be with its mother for seven days. From the eighth day and thereafter it may be favorably accepted as a sacrifice as a fire-offering to Hashem.
We are commanded that any cattle we bring as an offering is to be eight days old or more, and not less. This Mitzvah is also given in another form, viz., "Seven days it shall be with its mother" (Shemot 22.29). It applies to all offerings of all kinds, private and public. From the words, "From the eighth day and thereafter it may be favorably accepted as a sacrifice as a fire-offering to Hashem," it is concluded that before then it would not be acceptable. Therefore, it is clearly forbidden to offer an animal which has not reached the age of acceptability; but as this is a Negative Mitzvah derived from a Positive Mitzvah (P4), the penalty of whipping is not incurred for its transgressions, and he who brings [an offering] whose time has not come is not whipped.
Although by rights one should not sacrifice any animal before its is thirty days old, it is nevertheless deemed acceptable from eight days on; and even according to the strict letter of the law the firstling, the Pesach-offering and the tithe-offering of cattle may be offered as soon as they are eight days old. (Mishneh Torah, Avodah, Hilchot Maaseh HaKorbanot 1, 12).
In reference to the object of this Mitzvah, RaMBaM said, "This is the reason why no animal could be brought that was not yet seven days old, it is imperfect and repulsive, like an untimely birth" (Moreh Nevuchim 3, 46).