Erm, I suppose technically when I was about 10 months (dad gave me whisky to numb the pain in teething), but if actually drinking as a drink, about 10 and a couple of alcopops.
2% is fairly weak, one bottle of that shouldn't affect you too much, but I'd still drink slowly and with food if you've never drunk before. However, don't feel you have to drink - if you aren't comfortable drinking, then don't.