Praise be to Allaah.

Firstly: 

The scholars (may Allaah have mercy on them) are agreed that Islam has prescribed the age for sacrificial animals and it is not permissible to slaughter animals that are younger than that. Whoever slaughters an animal that is younger than that, it does not count as a sacrifice. 

See al-Majmoo’ by al-Nawawi, 1/176. 

For example, al-Bukhaari (5556) and Muslim (1961) narrated that al-Bara’ ibn ‘Aazib (may Allaah have mercy on him) said: A maternal uncle of mine whose name was Abu Burdah slaughtered his sacrifice before the prayer, and the Messenger of Allaah (peace and blessings of Allaah be upon him) said to him: “Your sheep is a sheep for meat (i.e., not a sacrifice).” He said: “O Messenger of Allaah, I have a young goat (according to another report: I have a young she-goat) (according to a report by al-Bukhaari (5563): I have a jadha’ah which is better than two musinnahs – shall I sacrifice it?)” The Prophet (peace and blessings of Allaah be upon him) said: “Sacrifice it, but that will not be valid for anyone but you.” According to another report: “It will not count for anyone after you.” Then he said: “Whoever slaughters (the animal) before the prayer has slaughtered it for himself, and whoever slaughters it after the prayer has offered the sacrifice and followed the way of the Muslims.” 

This hadeeth indicates that a jadha’ah of goats (young goat) is not sufficient as a sacrifice. We will explain below what jadha’ah means. 

Ibn al-Qayyim said in Tahdheeb al-Sunan: 

The phrase “It will not count for anyone after you” is a definitive statement that it would not count for anyone after him. End quote. 

Muslim (1963) narrated that Jaabir (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Do not slaughter anything but a musinnah, unless it is too hard for you, in which case you should slaughter a young sheep (jadha’ah min al-da’n). 

This hadeeth also clearly states that only a musinnah can be slaughtered, except in the case of sheep, where a jadha’ah may be offered. 

Al-Nawawi said in Sharh Muslim: 

The scholars said:   

A musinnah is a thaniyyah of anything, camel, cow or sheep, or anything over that age. This clearly indicates that it is not permissible to slaughter a jadha’ah of any animal in any circumstances, except sheep. End quote. 

Al-Haafiz said in al-Talkhees, 4/285: 

The apparent meaning of the hadeeth suggests that a jadha’ah of sheep is not permissible except if one cannot find a musinnah. Scholarly consensus says something different, so this hadeeth should be understood as referring to what is better. So it is mustahabb not to slaughter anything but a musinnah. End quote. 

Al-Nawawi said in Sharh Muslim: 

It says in ‘Awn al-Ma’bood: 

This interpretation is the one which is correct. End quote. 

Then he quoted some of the ahaadeeth which indicate that it is permissible to offer a jadha’ah of sheep as a sacrifice, such as the hadeeth of ‘Uqbah ibn ‘Aamir (may Allaah be pleased with him) who said: “We slaughtered a jadha’ah of sheep with the Messenger of Allaah (peace and blessings of Allaah be upon him).” Narrated by al-Nasaa’i, 4382. al-Haafiz said: Its isnaad is qawiy (strong). It was classed as saheeh by al-Albaani in Saheeh al-Nasaa’i. 

It says in al-Mawsoo’ah al-Fiqhiyyah (5/83) concerning the conditions of udhiyah: 

The second condition is that it should have reached the age of sacrifice, by being a thaniyyah or older in the case of camels, cows and goats, and jadha’ah or older in the case of sheep. A sacrifice does not count if the animal is younger than a thaniyyah except in the case of sheep, or if it is sheep that is younger than a jadha’ah…. The fuqaha’ are agreed upon this condition, but they differed as to what is meant by thaniyyah and jadha’ah. End quote. 

Ibn ‘Abd al-Barr (may Allaah have mercy on him) said: 

I do not know of any dissent with the view that a jadha’ah of goats or anything else that is offered as a sacrifice apart from sheep is not permissible. Rather it is permissible to sacrifice a thaniyyah or anything older than of all of these. It is permissible to sacrifice a jadha’ah of sheep according to the Sunnah. End quote from Tarteeb al-Tamheed, 10/267. 

Al-Nawawi said in al-Majmoo’ (8/366): 

The ummah is agreed that with regard to camels, cows and goats, nothing will do except a thaniyyah, and with regard to sheep, nothing will do but a jadha’ah, and that these are all acceptable. But some of our companions narrated that Ibn ‘Umar and al-Zuhri said: A jadha’ah of sheep does not count. It was narrated from ‘Ata’ and al-‘Awzaa’i that a jadha’ah of camels, cows, goats and sheep does count. End quote. 

Secondly: 

With regard to the stipulated age of sacrificial animals, the scholars differed concerning that. 

A jadha’ah of sheep is a sheep that has reached the age of six months, according to the Hanafis and Hanbalis. According to the Maalikis and Shaafa’is it is a sheep that has reached the age of one year. 

The musinnah (or thaniyyah) of goats is one that has reached the age of one year according to the Hanafis, Maalikis and Hanbalis. According to the Shaafa’is, it is one that has reached the age of two years. 

The musinnah of cows is one of the has reached the age of two years according to the Hanafis, Shaafa’is and Hanbalis; according to the Maalikis it is one that has reached the age of three years. 

The musinnah of camels is one that has reached the age of five years according to the Hanafis, Maalikis, Shaafa’is and Hanbalis. 

See Badaa’i’ al-Sanaa’i’, 5/70; al-Bahr al-Raa’iq, 8/202; al-Taaj wa’l-Ikleel, 4/363; Sharh Mukhtasar Khaleel, 3/34; al-Majmoo’, 8/365; al-Mughni, 13/368. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in Ahkaam al-Udhiyah: 

The thaniyyah of camels is one that has reached the age of five years. The thaniyyah of cows is one that has reached the age of two years. The thaniyyah of sheep is one that has reached the age of one year. The jadha’ah is one that has reached the age of half a year. It is not acceptable to offer anything younger than a thaniyyah in the case of camels, cows and goats, or anything younger than a jadha’ah in the case of sheep. 

It says in Fataawa al-Lajnah al-Daa’imah (11/377): 

The shar’i evidence indicates that a sheep that has reached the age of six months may count as a sacrifice, as may a goat that has reached the age of one year, a cow that has reached the age of two years, and a camel that has reached the age of five years.  Anything younger than that does not count as a hadiy or udhiyah. This is what the Qur’aan refers to when it says (interpretation of the meaning): “sacrifice a Hady (animal, i.e. a sheep, a cow, or a camel) such as you can afford” [al-Baqarah 2:196], because the texts of the Qur’aan and Sunnah explain one another. End quote. 

Al-Kaasaani said in Badaa’i’ al-Sanaa’i’ (5/70): 

These ages, as defined in sharee’ah, are minimum ages, not maximum ages. Sacrificing an animal that is younger than that is not permitted, but if an animal that is older than that is sacrificed, it is permitted and is better. It is not permitted to sacrifice a lamb, kid (young goat), calf or young camel, because the ages of animals that we have mentioned were narrated in sharee’ah and these were not mentioned among them. End quote. 

So it is clear that slaughtering a cow that is younger than two years old will not count as a sacrifice according to any of the imams. 

And Allaah knows best.