Well, allow me to chime in as well.
I grew up in a house and was told to stay away from just about everything. My mom is a lab tech, and would actually test my blood when I came home from a night out. The more forbidden they made something, the more I wanted to do it (and found a way). I snuck around alot, got frighteningly drunk on more than one occasion - all at the age of 15. I also became sexually active and started smoking pot. My parents told me to stay away from everything and forbade me from hanging out with the "bad" kids that they believe engaged in this stuff regularly.
All of my friends that had "looser" parents did less sneaking around, less drugs, and were reckless with alcohol to a much lesser degree (although I personally think that it is naive to think that they won't be in situations where they are doing this with their friends).
On another note, I also have friends that didn't drink at all when they were in high school - or before age 21, for that matter. However, when they became legal, they tried to make up for lost time. They had reached an age where most other "kids" had experience with alcohol, and knew how to handle themselves as a result. They, however, did not, and wound up getting sick and making fools of themselves on more than one occasion.
So the short answer is, I think you should let him try it. And, of course, make sure he is well educated on the dangers of drinking - both underage and in general - and also educate him on what to expect when he starts to feel drunk. In my opinion, most kids don't know their tipping point even in "safe" environments, and that is where the danger tends to lie.
I am boggled by the parents who actually buy alcohol for their Kids and will drink it with them. Parents and children must have boundries and it's up to the parent to set those boundries. Having an underage child as a drinking buddy erases all boundries and to draw the child's friends into it is criminal both literally and figuratively. 
