oneeyedjoe: It's probably not coming from watchtower specifically but any time you put yourself in a male-dominant authoritarian cult, you're probably going to find that women are viewed more as a commodity than for the person that they are (especially since they're not really allowed to express who they are and are instead required to be subservient) which will tend to favor younger women.
You are right.
The phenomena is a reflection of the male power position. The males have all the power in the JW cult and the women are objects to be possessed. By selecting and choosing "breeding age" women, favoring the sexually available and attractive woman, the men have defined sexuality as their priority and main focus. You could speculate that the average male JW is rather low on the evolutionary scale...they have not progressed past the point of living only within their animal nature