I do agree that even a few years can definitely make a lot of difference in an individual's maturity during the teen years. I had DC a few weeks after turning 16, and I can see that things would have been marginally easier if I'd been a year or two older, and a good deal harder if I'd been younger, so I don't disagree with that. However it still doesn't mean things can't turn out relatively OK, with the right support. I can only speak for myself, but I'm glad pregnancy lasts for 9 months, because teenage me presented with a newborn out of the blue would be very different from teenage me after 9 months of knowing it was going to happen.
The one thing I do know is that there is no "typical" teenage mother. Shared experiences, yes, but no one size fits all. The stereotype no doubt exists on a horrible sink estate somewhere, but she has bigger problems of which young parenthood is only one.
I don't like to sound as though I'm excusing or justifying teenage motherhood, it's not a path I expected to be on or one I would have chosen, but I don't believe people should be written off, and as a feminist, the double standards around teen girls having sex vs teen boys doing the same make me very cross. Actually, sometimes it feels that teen girls can do very little without having very high standards and harsh judgements applied to them
Teenagers can make all kinds of horrible mistakes. Grasp of consequences can be poor. Within my very naice schools I know, full of MC kids, there has been suicides, bullying drug use, self harm, abuse. The adolescent years can be so, so hard and teens can do awful, foolish things, to themselves and others. However it does seem that girls who get pregnant come in for a lot less sympathy than, for instance, a boy who is a habitual drug user and who becomes violent as a result.