[Lotus]

I suspect age and genetics are the two most prominent factors that influence areola size. My thoughts are that areola coincides with breast growth.

Hormones
The first thing to know is that breast development varies a great deal from person to person. Also while both age and genetics play a big role in how big they will get, generally speaking trans women can expect to be smaller then their closest female relatives (I was told a cup size smaller).

Besides the actual physical size of the breast, perception must be taken into consideration as well. The fact that the rib cage for the average anatomical male after puberty is bigger then it is for females means if you visually compare the two people with similar height, weight and bra size; one cissexual and one transsexual, the cissexual woman's breasts will generally appear larger. Also remember breast size in cissexual women varies greatly and not all cis woman have large breasts. I have small breasts and well... I like them.

http://sillytranswoman.blogspot.com/2011/01/male-to-female-breast-development.html