A few days ago a long list of university presidents recommended lowering the drinking age back to 18. I've seen several conservatives reject this out of hand but before passing judgment it is important to know why it is 21 in the first place.
First, the age of 21 is so deeply ingrained in our culture that few people even think about it. It is actually a magic number (7 + 7 + 7) and reflects prehistoric fascination with seven. You find seven occurring constantly in our culture, especially the older parts. Think about the days of the week, the wonders of the ancient world, deadly sins, etc.
Three was also important (think of the Trinity) which is why three sevens was so important. Six was less important but three sizes is where the importance of the age of eighteen came from.
In ancient times the ages of seven, fourteen, and twenty one were all important. Among medieval nobility boys became a page at seven, a squire at fourteen, and a knight at twenty one.
In modern times it was established that you became an adult at 21. When laws were passed to keep children from drinking (this is fairly recent), many of them set 21 as the lower limit. This was not universal. Some states allowed drinking at 18. When I was growing up, Ohio was split. You could buy beer with 3.2% or less alcohol at 18 but you had to be 21 to buy wine or spirits.
Then came Viet Nam and Nixon. In 1969 Nixon changed the draft. You registered at 18 and your number was drawn when you were 19. Because of this there was a push to give greater rights to youths. If you could die for your country you should be able to vote (the voting age was 21) and drink. Most states lowered their drinking age.
By the 1980s a new organization was founded - Mothers Against Drunk Driving (MADD). They are the modern equivalent to the temperance movement. They reasoned that people in the 18-25 range caused most drinking-related accidents. If they couldn't drink then the acident rate would plummet. It was politically impossible to raise the drinking age to 26 so they went for 21. Congress passed legislation mandating that states raise their drinking age or lose highway funds.
MADD also convinced Congress to lower the allowed blood alcohol level even though that was not a factor in most drinking-related deaths.
The lower drinking age has been a disaster for universities. When the drinking age was 18 then nearly all college students could drink legally. That meant going to bars where they would be cut off before they got "too" drunk. It also kept them in smaller groups and the sheer cost of drinking in a bar limited binges.
Now most college students are too young to drink but a significant number are allowed to buy alcohol. They pool their money and buy kegs then throw huge parties. There is no supervision so students (and non-students who show up) get roaring drunk. Since they are in large numbers, things get out of control quickly.
This has become a major problem across the country. At times partying at Ohio State (which is only a few miles from my house) has gotten bad enough to make Jay Leno's opening monologue.
At the same time, alcohol-related deaths in Ohio caused by underaged drinking has gone up. Raising the drinking age has had the opposite effect than intended.
There comes a time when you have to look at the consequences of actions like this and reevaluate them. Drinking in general and binge drinking has gone up because the drinking age was changed. The experiment failed. Lower it back to 18.