I have heard the medical explanation about nocturnal emissions, but I care for the spiritual dimensions. Must they be provoked by sexually arousing scenes in a dream and not the act? Is there anything spiritually unsafe? At what age will they stop? I still have wet dreams at the age of 28.
See "Is having a nocturnal emission (wet dream) a sin?" in regards to the spiritual aspects.
The way God designed the male body, there are several interconnected systems that come into play in order for a man to ejaculate. The brain is the coordinating system, so when the seminal vesicles signal they are full and need to be emptied, the brain starts a series of events to happen while you sleep. Since sexual action is going on, your dreams focus on sexual ideas. What your brain decides is connected with sex starts entering your dreams, which can become really strange because what you brain connects with sex might have little to do with actual sex. Or it can be images that you've seen over the years or things you imagined all which somehow got filed under the category of sex.
There is nothing you can do about those dreams since we aren't able to control our dreams. We can avoid putting junk into our brains, such as pornography, so that such doesn't appear in our dreams later, but that is about all the control we have.
Wet dreams only take place when your body needs to get rid of excess semen. When you get married and have regular sex with your wife, you won't have nocturnal emissions and the dreams that accompany them.