This is an accepted solution.
As per the "Account Terms" section of the Shopify Terms of Service, all persons using Shopify must be at least 18 years of age or "the age of majority in the jurisdiction where you reside". If you are under 18, I would suggest having a parent or guardian open a store under their name that you can help with and work on. Shopify cannot provide direct tax advice but I would presume in most jurisdictions, you would need to be 18 to register for and remit taxes. I would recommend consulting a tax professional if you are unsure of your obligations.
Victor | Shopify Social Care