I wanted a dog as a child too. My parents thought when I reached 12, I could learn to take care of pets. Some kids at 12 can handle a dog at that age and some need to be a bit older. It can vary. Have you ever had the responsibility of any pets?
I started with fish at 12 yrs of age, as did a few of my friends. They saw after 6 months or a year that I could handle it and gave me their permission to get a dog. However, because I was very involved with lots of after-school activities, I changed my mind about wanting a dog and stuck with fish.
Mind if I ask how old you are?