A: In Australia, the Corporations Act 2001 does not have a minimum age you have to have reached before you can be a shareholder of a company, so 14YO is a real possibility. It even has the possibility of a single shareholder/director under particular circumstances. But you don't have to be a company to do most things.
You can run your own business just with an ABN number, as a single person contractor. Contact the ATO to get your ABN and just get started.