What is the presumed age for giving testimony, and is the testimony of a discerning minor permissible?

Reaching puberty (bulugh al-hulm) is a prerequisite for a witness, due to the Almighty's saying: (And call to witness two just persons from among your men). A boy is not included among them. And due to the Almighty's saying: (from among those whom you deem fit to be witnesses). A boy is not deemed fit for testimony. And due to the Almighty's saying: (And whoever conceals it - his heart is sinful). A boy is not held accountable for sin. However, if a boy bears witness before reaching puberty and then delivers it after reaching puberty, it is accepted. There is also an opinion that accepts the testimony of boys in cases of injuries under certain conditions.