يُجْزِئُ فِي ذَلِكَ كُلِّهِ الثَّنِيُّ فَصَاعِدًا، إِلَّا مِنَ الضَّأْنِ فَإِنَّ الْجَذَعَ مِنْهُ يُجْزِئُ.
Translation: The thani or older qualifies, except a jadha‘ of sheep also qualifies.
Thani is a legal maturity term varying by species. The concession for a jadha‘ applies to sheep, not to a young goat.
The following slide explains the age benchmarks used in Hanafi legal commentaries.