Paul does speak of a moment that seems to have a sense that is similar to what is taught in the age of accountability:
Romans 7:9 Once I was alive apart from law; but when the commandment came, sin sprang to life and I died.
Yet it seems that Scripture teaches that people at all ages are accountable, Paul implies this here:
Romans 3:10 As it is written: “There is no one righteous, not even one…”
So then this would include even the youngest people, and with accountability (see Rom. 3:11-19).
So when Paul “died” when he heard the law and then coveted, there had still been accountability for sin before then, there is certainly loss of innocence when we first begin consciously sinning, but not a loss of exemption from accountability.
This also is indicated by the fact that people can respond to God even in the womb, as here:
PS 22:10 From birth I was cast upon you; from my mother’s womb you have been my God.
PS 71:6 From birth I have relied on you; you brought me forth from my mother’s womb.
And this would then imply accountability for going the opposite direction even at birth:
PS 58:3 Even from birth the wicked go astray; from the womb they are wayward and speak lies.
So all infants are not by definition sinless, the Jewish people of Jesus’ day believed that a person could sin and be accountable in his mother’s womb (John 9:2), and here is a Scriptural statement that is similar:
PS 51:5 Surely I was sinful at birth, sinful from the time my mother conceived me.
David is confessing his sins! That would seem to imply accountability for all these sins, even from the earliest age.
The Westminster Confession (10:3) speaks of some infants being saved, but not all: “Elect infants, dying in infancy, are regenerated, and saved by Christ, through the Spirit, who works when, and where, and how He pleases: so also are all other elect persons who are incapable of being outwardly called by the ministry of the Word.”
And this would seem to imply a view of accountability throughout the entire human life span.
“God may drop in grace, even with the first breathings of life, and regenerate a babe as soon as it be brought forth; as John Baptist, who was filled with the Holy Ghost, even from his mother’s womb (Lu 1:15). And others He may cast into the womb of the new birth when in the very act of dropping out of the world, at the eleventh, yea, at the twelfth hour, as the thief on the cross. Oh, who can order the ways of grace, and set bounds to the Spirit of God in its breathings on man!” (Christopher Ness)