I am currently twelve years old, In Australia, And I want to start making games, How old do you have to be to publish them on steam, or at least the app store ( I would prefer you answer the age for steam ) as a lot of users are probably on on windows and wont be able to buy a game on the mac app store, as thats what I use unity on. If someone could answer that would be great!
Depends on Australian law. You have to be old enough to enter legal contracts, and of course you also need be be old enough to open a bank account. In most countries, you have to be 18 to do these things.
You can make your parents or other people stand in for you, but this would also mean that they are the ones responsible if, for example, one of your published games violates copyright.