Remember: guardian angels are not mere mythology or the stuff of fairytales. They are efficacious ministers who help keep us safe on the path to eternal salvation. Devotion your angel isn’t something which should only take place when you are young. We need their protection at every age because at every age the devil tries to destroy us.
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, 1a, question 113, article 4)