D&C 84

The Lord revealed in modern day that -

"...John, whom God raised up, being filled with the Holy Ghost from his mother’s womb.
28 For he was baptized while he was yet in his childhood, and was ordained by the angel of God at the time he was eight days old unto this power, to overthrow the kingdom of the Jews, and to make straight the way of the Lord before the face of his people, to prepare them for the coming of the Lord, in whose hand is given all power."  (Doctrine and Covenants 84:27–28)

I've heard some say that John received the priesthood at eight days old.  But it is clear that an angel ordained, or blessed and set him apart at that age to overthrow the kingdom of the Jews and prepare for the coming of the Lord.