From what age can one recite the Orphan's Kaddish

From what age can one recite the Orphan's Kaddish?

It is customary to recite the Orphan's Kaddish even below the age of education, as long as the child can speak and recite the Kaddish properly, and is clean in body.

The Rema writes in Siman 376, paragraph 4: "But on weekdays, whoever knows how to pray should pray, and it is more beneficial than the Orphan's Kaddish, which was only instituted for minors; and whoever does not know how to pray the entire prayer," and so writes the Mishnah Berurah in Siman 132, SK 10. Therefore, the main institution is for minors who cannot pray as a chazan. The poskim have written that this is not related to the law of education, as it is not to accustom him to say Kaddish when he grows up, but because the Kaddish is for the elevation of his father's soul in place of the prayer he cannot say. Therefore, anyone who knows how to properly recite the Kaddish says it. And it is customary to have even the very young recite the Kaddish, as long as they know how to properly pronounce the words of the Kaddish and maintain bodily cleanliness.