Any modern newspaper editor would look at his opening salvo and say, "What a wonderful opening paragraph for this story!" Luke gives the who, what, where, and when right away, and gets to the why in short order. A complex scene is set out in order in just a few words.
Former Catholics will recognize verse 28 from the recitation of the rosary, "Hail, Mary, full of grace," taken from Jerome's Latin Vulgate, but the Greek does not read anything like that. Nor is there any authority to pray this to her. What the angel, Gabriel, really says to her is, "Rejoice, Mary, because you have found favor with God." She is so highly favored that the Lord blesses her, among all women on earth at the time, to be chosen for the honor of bearing and raising His Son.
Luke is actually suggesting, not that Mary should be adored for her favor with God, but that God should receive glory and adoration for bestowing such a blessing on her. He is the source of her favor; He gives it by grace to her, not because she was somehow qualified for it. She must have been a pretty good person, but she was not converted at the time. She was an ordinary Jewess of the line of David, though specially prepared for this blessing. Nevertheless, God displays His graciousness, not Mary's.
Most commentaries guess that she was about fourteen years old at the time, as that was the age when women commonly married then. Perhaps she was a little older. Tradition says that Joseph himself was an older man and might have desired a slightly older wife than was normal.
Verse 29 states that she was perplexed, agitated, or disturbed by what the angel said to her. She probably had no idea what to think, but to her credit, she did not become flighty or melt into a quivering mass. The Scriptures bring out that Mary was a serious thinker. In Luke 2:51, the evangelist tells us that she "kept all these things [concerning Jesus] in her heart," suggesting that she was patient, thoughtful, and wise. She did not jump to conclusions but let matters play out.