Not A Very Large Sample

Not A Very Large Sample

But it still doesn't say much for the situation, especially when you look at the average age they started. From the December 2, 2009 Telegraph:

Researchers were conducting a study comparing the views of men in their 20s who had never been exposed to pornography with regular users.
But their project stumbled at the first hurdle when they failed to find a single man who had not been seen it.
“We started our research seeking men in their 20s who had never consumed pornography,” said Professor Simon Louis Lajeunesse. “We couldn't find any.”
Although hampered in its original aim, the study did examined the habits of those young men who used pornography – which would appear to be all of them.
Prof Lajeunesse interviewed 20 heterosexual male university students who consumed pornography, and found on average, they first watched pornography when they were 10 years old.

This really is Generation Porn.