18, Australia (though as a culture we're pretty relaxed about teenagers starting to socially drink from around 16 under controlled circumstances). It would be absurd to have it higher than 18 - if you can be sent to war, and (more realistically for most) if we're going to demand that you take adult responsibility for crimes, then you've got to give adult autonomy as well.
I'm always amused by the irrationality of those that say 'we have to raise the drinking age / driving age' whilst also saying 'it shouldn't matter that the offender is 16, he should be tried as an adult!'. Can't have it both ways - make up your mind what age people have sufficient capacities to take adult responsibility, and then be consistent about it.