The aromatase enzyme is affected by a number of factors, not the least of which is simply genetics.
Factors known to increase aromatase activity include age, obesity, insulin, gonadotropins as affected by LH and other portions of the HPTA feedback loop, and alcohol (There is also a lot of debate about marijuana increasing activity as well, I personally don't see any evidence to support this, my guess is that most who smoke marijuana are just lazy and eat poorly, increasing adipose tissue and thus estrogen).
Aromatase activity is decreased by higher prolactin levels, higher AMH (Anti-Mullerian hormone) levels, and nicotine, all of which have negative effects as well for high levels. Some suggest that Omega-3 fatty acids reduce aromatase activity, but that is debatable as it doesn't really reduce or prevent aromatization, but rather reduces some of the notable side effects caused by aromatization.
