First, how do we define "good"? "good" and "bad" are subjective terms. We each have our own interpretation of these words and we each have our own ideas about what a "good" mother is. Therefore, discussing whether or not young women make "good" mother's is slightly silly as we will all have our own definition of "good". Also, you cannot generalize an entire group under one heading or another as there is a great propensity for variations within that group. You cannot say that all teen or young mother's are "good" mother's, you must instead view each young woman alone and not lump them all into the same category.
Secondly, given the facts and the world we live in today, it is much, much harder to be a young mother than it is for a woman who is older and more experienced. This is not to say that all young mother's are "bad" mother's it is only stating the fact that they encounter more problems due to their age and inexperience.
Thirdly, if you are doing the absolute best for your child and/or children no matter what your age, then why do you care what other people think? You know you are doing the best you can so whatever anyone else says is irrelevant.
Fourthly, each mother finds unique difficulties to her situation. The difficulties you face are not the same as another woman are facing. So comparing yourself to other women is pointless in this matter.
In my personal opinion, I do believe it is better to wait to have children. I am 22 and am still waiting to have children because now is not the right time. Does this mean that I think you were wrong for having children at a younger age? No. Does this mean I think you will make a "bad" mother? No. It only means that I can see the difficulties you are facing and know that it is not for me.