what Loc is saying is that you are too young to initiate a commercial contract.
That means
a) Your licence would effectively be invalid
b) If you sell anything as a commrcial enterprise you have to pay tax on it. (this is UK yeah), and for all that to be legal and above board, you need to register yourself as "self employed" at the Inland Revenue website. This means you will have to keep track of your sales, and if you make over £4000pa you will have to pay tax. You can register as self employed if you are out of compulsory education, ie, you are over 16.
if you're not over 16, then you would have to get your parent or guardian to sell the game for you... how will you recieve money anyway?!
I realise thats a total bummer, but there ya go.