How old do you have to be to start your own business?

I'm 16 years old and looking to start a business. I've been looking online and licenses and permits, but currently wondering if I have wasted time looking into equipment and permits when I may be too young. The business I was looking at was selling a product online (Starting a online shop). Do I need permits to start an online shop such as business license, trademark, copyright, registering the business, etc.. Also if I was able to start an online shop, could I also offline at places like a flea market and craft shows. Any Information will help. Thanks!