Is it fitting for each man to have an angel guardian?

"MAN while in this state of life, is, as it were, on a road by which he should journey towards heaven. On this road man is threatened by many dangers both from within and from without, according to Psalm 141:4: "In this way wherein I walked, they have hidden a snare for me." And therefore as guardians are appointed for men who have to pass by an unsafe road, so an angel guardian is assigned to each man as long as he is a wayfarer. When, however, he arrives at the end of life he no longer has a guardian angel; but in the kingdom he will have an angel to reign with him, in hell a demon to punish him."

~ St. Thomas Aquinas: Summa Theologica, I, q. 113, a. 4

Read more about guardian angels here

The Guardian Angel, by Pietro da Cortana. Oil on canvas, 1656;
Galleria Nazionale d'Arte Antica, Rome.

"Man has an angel guardian appointed to him"

"JEROME says (vide A, 4) that "each soul has an angel appointed to guard it from its birth." .... Origen observes (Tract. v, super Matt.) there are two opinions on this matter. For some have held that the angel guardian is appointed at the time of baptism, others, that he is appointed at the time of birth. The latter opinion Jerome approves (vide A, 4), and with reason. For those benefits which are conferred by God on man as a Christian, begin with his baptism; such as receiving the Eucharist, and the like. But those which are conferred by God on man as a rational being, are bestowed on him at his birth, for then it is that he receives that nature. Among the latter benefits we must count the guardianship of angels, as we have said above (1,4). Wherefore from the very moment of his birth man has an angel guardian appointed to him."

~St. Thomas Aquinas: Summa Theologica, I, Q. 113, A. 5.

See: Of the Guardianship of the Good Angels (Eight Articles)