Just because it's "research" and "published" doesn't mean it's right. I'm sure that there are opposing research saying that there is no correlation between age of exposure and criminal offenders.
Most likely the research fails to solidify causal relations, that MOST men who are exposed at age 14 become offenders, while failing to take into account parents, economic situation, education, and location.
It is possible for research to be flawed. However, if you contend THAT, it is now up to you to find debilitating flaws in it.
ALSO, on a more important note, the research in question did not claim that MOST men exposed at 14 or earlier become offenders.
It has been shown that people who were exposed to porn before reaching 14 are more likely offenders