Question 1123333
Assuming normality, z=(x-mean)/sd. 
<(40-51.4)/3.8 or < 3 sd s or probability is 0.0013
after age 55 would be z>3.6/3.4 or 1.058 or probability or 0.1450
age 30 is -21.4/3.8 or -5.63 sd
age 75 is 23.6/3.8 or 6.21 sd
By the time a woman has reached 75, she has essentially a 100% probability of having gone through menopause, assuming (not valid) she hasn't had a hysterectomy.  That's an important assumption to make.  Again, normality is important to assume as well, since there are potential statistical distributions (not necessarily valid in this population) that would have some reasonable non-zero probability of women not having gone through menopause.