what the legal age for drinking was
Be careful with the term "legal drinking age" because that actually means what age you can drink from at home with your parents. This is age 5 in England. In that case, the film over-estimated the age. What we are actually talking about is the legal age to either purchase or consume in bars and unlicensed properties.
It's interesting to see that both ages appear to be 21 in the USA.
http://www.grsproadsafety.org/themes/default/pdfs/Drinking%20Age%20Limits.pdf#search='legal%20drinking%20age%20at%20home'