I used to carry alcohol all the time between Spain and the UK as an unaccompanied minor. The alcohol would be gifts from family and friends in Spain to my parents. I was pulled up once about it, my parents had to pay the duty (my brother and I were schlepping well over anyone's allowance) but it wasn't confiscated.

If you're concerned that customs could seize it, couldn't someone 'responsible' for you come to collect you at the airport? My thinking is that if they have a problem with a minor being in possession of alcohol, they could perhaps hand it to someone at the gate instead.