There is a Law in the books prohibiting vendors to sell alcoholic beverages to persons under 18 years of age, in effect since January of 2006.  But as many other things in China, no one pays any attention to it.

The same occurs in regards to persons under 18 years of age drinking alcoholic beverages in public.   Or smoking.

As an item of interest, the only country in the world that does prohibit minors from drinking alcoholic beverages in public AND AT HOME, is the UK.

there is no one care about how old you are when you buy alcohol. in China, even a child may drink alcohol if his parents don't care.