This song reduced me to tears. Seriously. You guys, if ya don't want to listen to it but, it is a good song with a good message.
So basically, this girl's father is never there and doesn't seem to love her. THis is in the 16th birthday section.
In the 19th birthday section, the girl had a boyfriend that they both thought that each were the one for each other... or at least the girl did. She becomes pregnant and, the guy leaves her in the dust.
The rest of the song is basically telling how she wants someone to help her feel whole again. And wants Jesus to help her. She explicitly says that she wants God to be like a father figure for her baby.
When she's 21, she has her little girl and is thankful for God for giving the girl's daughter to her. And, the girl is basically the main girl's new birthday.
Oh my gosh, it makes me so mad that so many people go through this exact thing but... then like in this song, usually it comes out to be alright. And they find the joy through all of their sadness.