Quote Originally Posted by Northumbrian
That isn’t a problem, because in the UK, legally, anything with ABV (alcohol by volume) of less than 1.2% is classed as a soft drink. Bottled shandies and (some) brewed ginger beers are alcoholic. These “soft drinks” usually have an ABV of 0.5%. So you’d have to drink ten pints of the stuff to get the alcohol equivalent of a pint of beer.
It is the same in Canada and the US. All soft drinks, Cola, Pepsi, Cream soda, you name it, has mild alcohol. It's just from the way it's made that it ends up like that. It just doesn't say it on the label. A fact I learned from Steven Colbert and his useless/hilarious news updates.

So I'm guessing Butterbeer is pretty much the same. Safe for anyone to drink, other than house elves, but still has some alcohol in it. I would agree with everyone else that the age to drink would be 17. Or, the age to buy a drink legally would be 17, as Northumbrain also stated that Ginny was drinking Firstwhisky at 15.