This is a data note linked to an ongoing discussion on the NBR Japan Forum. See the related post below (the oldest one on the blog).
Female labor force participation has been rising monotonically in the immediate post-schooling age brackets, beginning with the age 25-29 cohort and now very visibly extending to the age 30-34 cohort.
But let's not get too excited about this as a means to offset the rise in the number of retirees. [And as to that, the immediate post-WWII "baby boom" cohorts begin retiring en masse in 2012-2013: we haven't seen anything yet!] As the graph below highlights, while almost 80% of young women age 24-29 now are in the labor force, up 30+ percentage points from 1975, the total number of young women working is falling. Rising female LF participation is unable to offset the absolute fall in the size of the labor force, it can at most slow it modestly.