I'd suggest that you try babysitting. Having your own kid, especially at your age, could be something you're unable to support as others have said. Also your body most likely isn't ready for it; for example your hips may not be wide enough and you don't want to have a scare on your belly.
I have a baby niece and she spent more time with me than anyone else back before I came to college this month. It's amazing to see how kids take after you as they grow, and they can be fun when they're not in bad moods. However this doesn't mean you have to have a baby to experiance this.
I'd suggest you try babysitting. You may have a young cusion or anyone really that you could watch or even help take care of with the parents. If a neighbor your family is friends with has a kid then ask them if you could ever help out or babysit; even if you had to do it under supervision of your parents until you gain their trust.
Then, when you're sixteen you could get a job at a daycare center. My high school had a class where all you did was take care of the babies in their daycare for students with babies, and that you can start your freshman year.