All these Americans saying it's illegal for you to drink at 20 obviously have no idea about the laws of their own country.
Then again we get the same in the UK, where it is legal to drink in the home as long as it is under parental supervision from 5, and legal to drink in pubs/restaurants if having a meal (again under parental supervision) from 16.
Yet we still get people who don't know the laws here (Jims answer is a perfect example - you can NOT buy alcohol with a meal at 16, you can drink with a meal if you are eating it with a parent/guardian at that age but can not buy it yourself, he is also incorrect on drinking in the home - the law states that giving alcohol to anyone under 5 years old, except for medicinal purposes, is illegal.).
The ages stated in both countries are the legal age to PURCHASE ALCOHOL, not drink it under supervision (unless you are in Utah)