As a person who listens to gates' music and Walls Talking being one of my favorite songs, I have to step in and defend this

Gates was mostly raised by his grandma. So when he says that line it's pose to be like "I was young, when my mama had me, I ran away when ran away at 15"
He said it to fit with rhyme (me/15) but also letting those who know he was raised by his grandma, that this happened when he was staying with his mom.