The perfect age for a woman to have a baby is when she is emotionally and mentally ready to have one, there is no magic age. It takes a lot of sacrifice to raise a baby. Anyway I think each woman is different because we all mature at different rates.
There is no such thing universally. However , objectively it would be when you are emotionally ready, when you want one, when you can afford to have one without government help, when you have someone in your life who will be there to raise it with you.
I had my child at 24, which was the perfect age for me and my husband, because we had an established strong relationship, we were financially prepared and we were both emotionally ecstatic that we were going to have a baby. Now that my daughter is in daycare, I feel old...it seems like babies are having babies these days and despite the fact that I think 24 was young to have a child, I feel like I'm lumped into that "older mom" group compared to the parents of most of the children in her day care.