How can I convince my parents to decide to get me a dog?

When I was about nine months old my family got a chocolate lab from a farm for $20. I grew up with her and she was my best friend. I was her main owner. I fed her and took her for walks, etc. On the 19th of June last year she sadly passed away of several strokes. I was distraught, and I felt like my sister had died. After a period of " mourning" I think I'm ready for another dog. I've asked my parents to adopt from a shelter to save a life, and I've proven that I was responsible. My parents have said no. What is a mature way to change their minds?

There is no mature way. Kids don't seem to realize that the parents are the ones paying the bills, so they get to choose what lives in their house. You're just going to have to wait until they change their minds, or you get a house of your own.

Your parents obviously have their minds made up about getting a dog. They have their reasons. You are living in your parents home and you need to listen and follow their rules. The more you bug them about getting a dog, the more angry they will become with you and they will still say NO. Dogs are very expensive and they are a lot of responsibility. Your parents are going to be the ones who will be providing everything for the dog including regular vet care and they are going to be the ones that end up taking care of your dog. When you get your own place, you can get any kind of dog that you want. Until then,what your parents say goes.

Tell them by getting another dog it will help you heal the hurt you suffered when your 1st dog died. Tell them that getting a dog will help you in your sorrow and will help the dog because it will be getting a loving and safe home. I hope they let you get it.