If marijuana is legal, what should be the minimum age for smoking it?

[angus]

I don't know enough about the science of marijuana use and adolescent brain development to give an informed answer to this question.

Neither did Jean Piaget, but that didn't stop him from becoming famous and providing a great deal of misinformation to a generation of psychologists.

[angus]

What did Piaget have to say about marijuana?

Well, for starters he felt like the frontal lobe was pretty much developed by the age of 12.  Nowadays 25 is the more commonly cited age for full development.  

Nowadays there are many studies you can read about the effect of marijuana and alcohol on developing brains.  Piaget didn't have that luxury.  

I actually voted for 18 as well, but it's pretty arbitrary.  Whether most kids at that age are really ready to vote, drive, drink booze, smoke pot, or make war is something I'm not sure about, but it seems to be ingrained in our society that this is the age of consent so that's what I chose in this poll.  Same as I selected in the drinking age poll last December.

[angus]

The fact that the medical marijuana groups actually opposed full legalization in every state that's voted on it so far has obviously not been taken into account.

It has been taken into account plenty by journalists.  In fact, a number of stories have been written about the fact that the marijuana growers associations in California are some of the biggest opponents of legalization.  I can remember such stories appearing for at least four years (and my memory is pretty bad, with all the weed that I smoked as a high school student, so they have probably been around much longer.)