JOEL - It does sound sexist, but according to my wife it's because the women can get more accomplished in a shorter amount of time compared to the young men :-) Also its because full-time missionary work is primarily the responsibility for the men, so the women are asked to serve for a shorter time. At one time the women also served for two years, but since the women don't serve until they are 21 years old, I believe the church leaders felt it was important for them to serve a shorter time so they are able to get home and start a family before they got much older. Extensions are not granted and sisters don't ask for them because they already know this before they begin their missions.
However, according to a former sister missionary: "I found out on my mission that even though a sister can only serve for 18 months she can go on as many missions as she can afford before she is married, when she and her husband have retired, and after her husband has passed on. An Elder can only serve once before he is married, as many times as he can afford after he and his wife are retired, but he cannot serve a mission after his wife dies. Since A guy can only serve one time as a single but a girl can serve many times I decided sexism has nothing to do with it, it's just how the Lord wants it done." (Joy)
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