It is permissible to slaughter a goat, sheep, cow, bull, buffalo or camel, male or female for Qurbani.
The minimum age of:
(a) A goat, sheep, or ram is one full year,
(b) A cow, bull or buffalo is two years old, and
(c) A camel five years.
• Animals that are younger than the prescribed age are not suitable for Qurbani. (Fataawa Hindiyyah)

• If a sheep is more than six months old but less than a year, and physically appears to be one year old it will suffice for Qurbani. (Fatawa Hindiyyah)

• A cow, bull, buffalo or camel will suffice for seven persons provided no one’s share is less than one seventh and the niyyah (intention) of all partners is to attain reward and not merely to obtain meat. (Fatawa Shaamiyah)
عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ، قَالَ حَجَجْنَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم فَنَحَرْنَا الْبَعِيرَ عَنْ سَبْعَةٍ وَالْبَقَرَةَ عَنْ سَبْعَةٍ
Jabir b. ‘Abdullah (Allah be pleased with him) reported:

We performed Hajj along with Allah’s Messenger (ﷺ), and we sacrificed a camel on behalf of seven persons, and a cow on behalf of seven persons. [Sahih Muslim 1318]

• A goat, sheep or ram will suffice for the Qurbani of one person only. (Fatawa Hindiyyah)

• It is permissible and preferable to slaughter a castrated animal. (Fatawa Mahmoodiyah)

• It is advisable to purchase the Qurbani animal a few days prior to slaughtering in order to build up some form of attachment with the animal by taking care of it. (Fatawa Hindiyyah)

• Animals chosen for Qurbani should be healthy, free from faults and defects. (Fatawa Shaamiyah)