"Having kids so young"

I'm 21, happily married, and ready to build our family. I'm pregnant with my first, about 13 weeks. So many people have told me I'm too young, that I'm still a child myself, and that I won't be a good mother because of it. I have a full time, well-paying job, my own paid for car, and my husband and I are $11,000 from owning our house. I feel like I'm healthy, energetic, and more than mature enough to raise my baby. It seriously saddens me how much people look down on me for wanting a baby at this point in my life.