I thought this could be interesting. We'll see. I'll try to find estimates of the general population. You're invited to do the same.
Yow, I looked into Wikipedia. I am way behind my quota. To me, the most shocking thing are 50 year old married guys still having maybe 8 a year, on average. I haven't had more than 5 total in my entire life.
You can see the results of an online wet dream poll.http://www.misterpoll.com/polls/265759/results
The All Knowing Wikipedia says:https://secure.wikimedia.org/wikipedia/en/wiki/Nocturnal_emission
The frequency of nocturnal emissions is highly variable. Some men have experienced large numbers of nocturnal emissions as teenagers, while others have never experienced one. 83% of men in the United States will experience nocturnal emissions at some time in their life.
 For males who have experienced nocturnal emissions the mean frequency ranges from 0.36 times per week for single fifteen-year-old males
to 0.18 times per week for forty-year-old single males
. For married males the mean ranges from 0.23 times per week for nineteen-year-old married males
to 0.15 times per week for fifty-year-old married males
. In some parts of the world nocturnal emissions are more common. For example in Indonesia surveys show that 97% of men experience nocturnal emissions by the age of twenty four