In the UK as with most of the EU the tax you pay is purely a percentage of what you bring in.
Therefore if your game makes nothing you pay no tax.

This only applies to sole traders as a limited company (gmbh etc) will have to pay corporation tax.

Also once you earn enough you have to pay various taxes like PAYE (depending on country, e.g. here in the UK) and if you earn a lot you can claim your VAT back (for the Americans, this is similar in some ways to sales tax).

In Denmark at least you can't transfer a sole trader company, you'll need to create an LLC if you wish to transfer ownership. Here a sole trader business is just an extension of yourself. Not something you can transfer or sell.

I would suggest you to get one of your parents to register a company, there should be an option for creating a company for free (I know most countries have that at least). Then they can transfer it back to you later. Also if you live near a big town, there should be some incubators or just a general startup/inventor community, where I think you would be able to find someone willing to give you some advice :) (but try not to give them the rights to your company, better to have that with your own parents (assuming you can trust them..))