I want to design a car concept. Where do I start?

I'm 13. I know I'm young. It won't go through. I'm not looking to submit it yet but to make a work in progress I can look at later on in life. This is my dream. I want to design a modern day Ford Thunderbird performance concept car. Please be nice. This is what I want to do with my life. I want to become an auto-mechanic engineer and designer.

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