How much alcohol does it take a 12 year old person to get drunk?

Well, it is illegal to find out!

And it depends on your definition of drunk. Alcohol starts to affect judgment very quickly, for most people two drinks (beer, wine, mixed drinks) will have an effect. Smaller people like a 12 year old will be more affected faster. The person's weight, the amount of food they have eaten recently and the rate at which they drink the alcohol all affect the results.

Anyone that supplies alcohol, allows a minor to consume alcohol can be subject to criminal presecution.