Which time of our lives are Guardian Angels assigned to protect us?

Guardian Angels appeared throughout Scripture, for instance in the book of Judith where she says that God’s “angel hath been my keeper” (Judith 13:20).
Jesus also taught his disciples about the existence of Guardian Angels when speaking about the protection of little children in Mathew (Matt. 18:10), “See that you do not despise one of these little ones; for I tell you that in heaven their angels always behold the face of my Father who is in heaven”.
Though not clearly revealed in Scripture, but it is generally believed by theologians that all human beings, whether they are Christian or not, have been assigned a Guardian Angel.
Pope Pius XII in one of his addresses related how, “Everyone, no matter how humble he may be, has angels to watch over him.” This is dependent with the Sacred Scripture, the teachings of Sts. Thomas Aquinas, the teachings of Basil, and Jerome, and also the experiences from non-Christians who believe they were helped by a Guardian Angel.
So, if everyone are assigned a Guardian Angel, when does this assignment take place?
The only statement that is official about the timing of this assignment comes from the Catechism of the Catholic Church (CCC 336), which says, “From its beginning until death, human life is surrounded by their watchful care and intercession. ‘Beside each believer stands an angel as protector and shepherd leading him to life”.
This particular statement is not precise and it simply points to the “onset” of human life.
Over the centuries, theologians have debated about the exact moment of this assignment and there still exist multiple views.
For instance, St. Jerome simply puts, “how great is the dignity of the soul, since each being has been commissioned an angel from his birth to guard it.”
Based on the scientific knowledge this was a popular opinion for many centuries, which they possessed at the time.
Furthermore, St. Anselm says “Every soul is committed to an angel at the time when it is united with a body.” As this also is debated among theologians, many still believe that this takes place at conception.
According to a Vatican document which was compiled by Cardinal Joseph Ratzinger in 1987, “the spiritual soul of each man is created by God immediately.”
Hence, it follows that a Guardian Angel is seem to be appointed at the moment of conception. This is not a dogmatic belief of the Catholic Church, but it appears to follow from other teachings that have been handed down over the centuries, and would be consistent with the words of Jesus in the Gospel of Matthew.
Even if a person’s Guardian Angel isn’t assigned at conception, the mother’s Guardian Angel would be automatically put in charge of the developing human being which is inside the womb.
Whether we notice it or not, the fact is that from the very on set of our lives we are surrounded by heavenly angels who their work is to protect us from all spiritual and physical harm.
So we have the free will to allow them to do their jobs or we can as well cut ourselves off from their protecting help. It is also a profound mystery, one that we can never fully understand until we finally meet our Guardian Angel in the life to come.