Congratulations on starting your Shopify store. As @Bunty mentioned, it is stated in our Terms of Service under Account Terms that:
You must be the older of: (i) 18 years, or (ii) at least the age of majority in the jurisdiction where you reside and from which you use the Services to open an Account.
There is a great thread about this topic in our Community linked here. In order to start a Shopify store, you will require someone (typically a parent or legal guardian) who meets these terms to create and manage the Shopify account for you, until you become of age to manage the account yourself. You can follow our help document on transferring account ownership here.
Let me know if you have any further questions!