I don't understand how you could be too immature to make a decision about abortion but mature enough to have a child, but that's my personal confusion.
Let's clear this up. Mature or not, abortion is never acceptable. But as it pertains to young women, they may be more likely to make rash, irreversable decisions because they often lack the wisdom and knowledge that comes from experiencing life. I would never say that a teen is mature enough to have a child, but they are definitely in a place to learn from their mistakes. 20 years from giving birth, they can at least live without the guilt of killing their offspring, and perhaps without the physical repercussions of having had an abortion.
Pregnancy is an irreversible situation, but abortion isn't a corrective. It doesn't change the fact that the pregnancy occurred, it only kills the child. Abortion isn't a mistake we want to encourage young women to make, it's a decision only they have to live with.